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 $176.75   9.180%   $192.9757   $192.98   $193.00   $193.00  
  Purchase #2 $212.42   12.481%   $238.9321   $238.93   $238.95   $238.90  
  Purchase #3 $201.41   11.386%   $224.3425   $224.34   $224.35   $224.30  
  Purchase #4 $127.41   13.413%   $144.4995   $144.50   $144.50   $144.50  
  Purchase #5 $41.84   9.648%   $45.8767   $45.88   $45.90   $45.90  
  Purchase #6 $160.86   12.146%   $180.3981   $180.40   $180.40   $180.40  
  Purchase #7 $248.34   12.523%   $279.4396   $279.44   $279.45   $279.40  
  7 purchase totals = $1,169.03       $1,306.4642   $1,306.47   $1,306.55   $1,306.40