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 $114.80   3.679%   $119.0235   $119.02   $119.00   $119.00  
  Purchase #2 $170.48   3.507%   $176.4587   $176.46   $176.45   $176.50  
  Purchase #3 $181.45   9.112%   $197.9837   $197.98   $198.00   $198.00  
  Purchase #4 $68.36   8.236%   $73.9901   $73.99   $74.00   $74.00  
  Purchase #5 $35.73   11.657%   $39.895   $39.90   $39.90   $39.90  
  Purchase #6 $149.55   12.850%   $168.7672   $168.77   $168.75   $168.80  
  Purchase #7 $221.89   10.397%   $244.9599   $244.96   $244.95   $245.00  
  7 purchase totals = $942.26       $1,021.0781   $1,021.08   $1,021.05   $1,021.20