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 $57.32   9.188%   $62.5866   $62.59   $62.60   $62.60  
  Purchase #2 $105.27   11.108%   $116.9634   $116.96   $116.95   $117.00  
  Purchase #3 $219.64   6.257%   $233.3829   $233.38   $233.40   $233.40  
  Purchase #4 $53.52   13.307%   $60.6419   $60.64   $60.65   $60.60  
  Purchase #5 $247.26   5.427%   $260.6788   $260.68   $260.70   $260.70  
  Purchase #6 $24.97   12.819%   $28.1709   $28.17   $28.15   $28.20  
  Purchase #7 $38.71   6.832%   $41.3547   $41.35   $41.35   $41.40  
  7 purchase totals = $746.69       $803.7792   $803.77   $803.80   $803.90