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 $48.97   12.345%   $55.0153   $55.02   $55.00   $55.00  
  Purchase #2 $235.67   12.698%   $265.5954   $265.60   $265.60   $265.60  
  Purchase #3 $61.33   12.704%   $69.1214   $69.12   $69.10   $69.10  
  Purchase #4 $123.56   6.477%   $131.563   $131.56   $131.55   $131.60  
  Purchase #5 $217.36   4.141%   $226.3609   $226.36   $226.35   $226.40  
  Purchase #6 $180.74   6.266%   $192.0652   $192.07   $192.05   $192.10  
  Purchase #7 $91.49   13.506%   $103.8466   $103.85   $103.85   $103.80  
  7 purchase totals = $959.12       $1,043.5678   $1,043.58   $1,043.50   $1,043.60