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 $224.48   8.234%   $242.9637   $242.96   $242.95   $243.00  
  Purchase #2 $48.36   8.846%   $52.6379   $52.64   $52.65   $52.60  
  Purchase #3 $100.52   7.103%   $107.6599   $107.66   $107.65   $107.70  
  Purchase #4 $108.98   4.234%   $113.5942   $113.59   $113.60   $113.60  
  Purchase #5 $144.29   6.677%   $153.9242   $153.92   $153.90   $153.90  
  Purchase #6 $30.52   5.247%   $32.1214   $32.12   $32.10   $32.10  
  Purchase #7 $245.43   7.631%   $264.1588   $264.16   $264.15   $264.20  
  7 purchase totals = $902.58       $967.0601   $967.05   $967.00   $967.10