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 $203.78   3.549%   $211.0122   $211.01   $211.00   $211.00  
  Purchase #2 $96.31   11.441%   $107.3288   $107.33   $107.35   $107.30  
  Purchase #3 $20.66   6.507%   $22.0043   $22.00   $22.00   $22.00  
  Purchase #4 $235.33   6.604%   $250.8712   $250.87   $250.85   $250.90  
  Purchase #5 $232.82   3.250%   $240.3867   $240.39   $240.40   $240.40  
  Purchase #6 $101.79   10.550%   $112.5288   $112.53   $112.55   $112.50  
  Purchase #7 $116.33   9.356%   $127.2138   $127.21   $127.20   $127.20  
  7 purchase totals = $1,007.02       $1,071.3458   $1,071.34   $1,071.35   $1,071.30