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 $71.39   6.137%   $75.7712   $75.77   $75.75   $75.80  
  Purchase #2 $211.39   4.192%   $220.2515   $220.25   $220.25   $220.30  
  Purchase #3 $62.75   13.427%   $71.1754   $71.18   $71.20   $71.20  
  Purchase #4 $201.37   9.861%   $221.2271   $221.23   $221.25   $221.20  
  Purchase #5 $200.28   5.118%   $210.5303   $210.53   $210.55   $210.50  
  Purchase #6 $119.51   13.400%   $135.5243   $135.52   $135.50   $135.50  
  Purchase #7 $38.35   3.176%   $39.568   $39.57   $39.55   $39.60  
  7 purchase totals = $905.04       $974.0478   $974.05   $974.05   $974.10