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 $54.65   7.839%   $58.934   $58.93   $58.95   $58.90  
  Purchase #2 $228.32   3.287%   $235.8249   $235.82   $235.80   $235.80  
  Purchase #3 $27.93   11.561%   $31.159   $31.16   $31.15   $31.20  
  Purchase #4 $164.30   13.863%   $187.0769   $187.08   $187.10   $187.10  
  Purchase #5 $95.51   13.334%   $108.2453   $108.25   $108.25   $108.20  
  Purchase #6 $182.90   4.837%   $191.7469   $191.75   $191.75   $191.70  
  Purchase #7 $75.84   7.375%   $81.4332   $81.43   $81.45   $81.40  
  7 purchase totals = $829.45       $894.4202   $894.42   $894.45   $894.30