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 $34.94   3.817%   $36.2737   $36.27   $36.25   $36.30  
  Purchase #2 $144.96   13.722%   $164.8514   $164.85   $164.85   $164.90  
  Purchase #3 $210.72   5.363%   $222.0209   $222.02   $222.00   $222.00  
  Purchase #4 $120.89   7.282%   $129.6932   $129.69   $129.70   $129.70  
  Purchase #5 $182.51   10.478%   $201.6334   $201.63   $201.65   $201.60  
  Purchase #6 $94.38   8.529%   $102.4297   $102.43   $102.45   $102.40  
  Purchase #7 $209.60   5.345%   $220.8031   $220.80   $220.80   $220.80  
  7 purchase totals = $998.00       $1,077.7054   $1,077.69   $1,077.70   $1,077.70