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 $54.85   8.759%   $59.6543   $59.65   $59.65   $59.70  
  Purchase #2 $167.84   4.218%   $174.9195   $174.92   $174.90   $174.90  
  Purchase #3 $19.30   8.357%   $20.9129   $20.91   $20.90   $20.90  
  Purchase #4 $120.91   6.719%   $129.0339   $129.03   $129.05   $129.00  
  Purchase #5 $133.81   6.676%   $142.7432   $142.74   $142.75   $142.70  
  Purchase #6 $159.91   8.507%   $173.5135   $173.51   $173.50   $173.50  
  Purchase #7 $82.74   5.706%   $87.4611   $87.46   $87.45   $87.50  
  7 purchase totals = $739.36       $788.2384   $788.22   $788.20   $788.20