Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $110.94   7.861%   $119.661   $119.66   $119.65   $119.70  
  Purchase #2 $236.37   9.692%   $259.279   $259.28   $259.30   $259.30  
  Purchase #3 $133.32   8.837%   $145.1015   $145.10   $145.10   $145.10  
  Purchase #4 $246.39   12.789%   $277.9008   $277.90   $277.90   $277.90  
  Purchase #5 $226.36   13.377%   $256.6402   $256.64   $256.65   $256.60  
  Purchase #6 $156.65   8.787%   $170.4148   $170.41   $170.40   $170.40  
  Purchase #7 $142.45   9.710%   $156.2819   $156.28   $156.30   $156.30  
  7 purchase totals = $1,252.48       $1,385.2792   $1,385.27   $1,385.30   $1,385.30