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 $169.46   11.582%   $189.0869   $189.09   $189.10   $189.10  
  Purchase #2 $196.57   10.775%   $217.7504   $217.75   $217.75   $217.80  
  Purchase #3 $44.43   10.406%   $49.0534   $49.05   $49.05   $49.10  
  Purchase #4 $127.28   10.614%   $140.7895   $140.79   $140.80   $140.80  
  Purchase #5 $68.52   3.351%   $70.8161   $70.82   $70.80   $70.80  
  Purchase #6 $179.41   13.327%   $203.32   $203.32   $203.30   $203.30  
  Purchase #7 $136.34   12.536%   $153.4316   $153.43   $153.45   $153.40  
  7 purchase totals = $922.01       $1,024.2479   $1,024.25   $1,024.25   $1,024.30