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 $32.46   6.606%   $34.6043   $34.60   $34.60   $34.60  
  Purchase #2 $51.30   10.282%   $56.5747   $56.57   $56.55   $56.60  
  Purchase #3 $152.77   10.633%   $169.014   $169.01   $169.00   $169.00  
  Purchase #4 $219.59   13.743%   $249.7683   $249.77   $249.75   $249.80  
  Purchase #5 $74.76   3.484%   $77.3646   $77.36   $77.35   $77.40  
  Purchase #6 $208.50   8.260%   $225.7221   $225.72   $225.70   $225.70  
  Purchase #7 $133.80   12.612%   $150.6749   $150.67   $150.65   $150.70  
  7 purchase totals = $873.18       $963.7229   $963.70   $963.60   $963.80