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 $49.51   8.385%   $53.6614   $53.66   $53.65   $53.70  
  Purchase #2 $193.75   11.813%   $216.6377   $216.64   $216.65   $216.60  
  Purchase #3 $154.64   11.854%   $172.971   $172.97   $172.95   $173.00  
  Purchase #4 $223.32   12.171%   $250.5003   $250.50   $250.50   $250.50  
  Purchase #5 $42.47   6.614%   $45.279   $45.28   $45.30   $45.30  
  Purchase #6 $250.41   8.695%   $272.1831   $272.18   $272.20   $272.20  
  Purchase #7 $146.73   5.617%   $154.9718   $154.97   $154.95   $155.00  
  7 purchase totals = $1,060.83       $1,166.2043   $1,166.20   $1,166.20   $1,166.30