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 $176.99   10.290%   $195.2023   $195.20   $195.20   $195.20  
  Purchase #2 $134.35   11.581%   $149.9091   $149.91   $149.90   $149.90  
  Purchase #3 $37.82   9.701%   $41.4889   $41.49   $41.50   $41.50  
  Purchase #4 $70.62   9.690%   $77.4631   $77.46   $77.45   $77.50  
  Purchase #5 $94.49   11.146%   $105.0219   $105.02   $105.00   $105.00  
  Purchase #6 $91.45   3.339%   $94.5035   $94.50   $94.50   $94.50  
  Purchase #7 $129.39   4.573%   $135.307   $135.31   $135.30   $135.30  
  7 purchase totals = $735.11       $798.8958   $798.89   $798.85   $798.90