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 $49.76   9.445%   $54.4598   $54.46   $54.45   $54.50  
  Purchase #2 $210.26   11.290%   $233.9984   $234.00   $234.00   $234.00  
  Purchase #3 $45.54   6.550%   $48.5229   $48.52   $48.50   $48.50  
  Purchase #4 $184.68   7.152%   $197.8883   $197.89   $197.90   $197.90  
  Purchase #5 $134.36   3.692%   $139.3206   $139.32   $139.30   $139.30  
  Purchase #6 $243.33   10.363%   $268.5463   $268.55   $268.55   $268.50  
  Purchase #7 $95.32   12.360%   $107.1016   $107.10   $107.10   $107.10  
  7 purchase totals = $963.25       $1,049.8379   $1,049.84   $1,049.80   $1,049.80