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 $127.79   9.645%   $140.1153   $140.12   $140.10   $140.10  
  Purchase #2 $244.40   11.822%   $273.293   $273.29   $273.30   $273.30  
  Purchase #3 $186.45   4.330%   $194.5233   $194.52   $194.50   $194.50  
  Purchase #4 $148.40   10.837%   $164.4821   $164.48   $164.50   $164.50  
  Purchase #5 $84.30   7.162%   $90.3376   $90.34   $90.35   $90.30  
  Purchase #6 $152.70   11.369%   $170.0605   $170.06   $170.05   $170.10  
  Purchase #7 $163.63   10.199%   $180.3186   $180.32   $180.30   $180.30  
  7 purchase totals = $1,107.67       $1,213.1304   $1,213.13   $1,213.10   $1,213.10