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 $99.96   12.556%   $112.511   $112.51   $112.50   $112.50  
  Purchase #2 $202.72   13.242%   $229.5642   $229.56   $229.55   $229.60  
  Purchase #3 $87.61   6.682%   $93.4641   $93.46   $93.45   $93.50  
  Purchase #4 $23.40   6.673%   $24.9615   $24.96   $24.95   $25.00  
  Purchase #5 $129.84   4.596%   $135.8074   $135.81   $135.80   $135.80  
  Purchase #6 $9.90   7.508%   $10.6433   $10.64   $10.65   $10.60  
  Purchase #7 $93.67   9.360%   $102.4375   $102.44   $102.45   $102.40  
  7 purchase totals = $647.10       $709.3890   $709.38   $709.35   $709.40