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 $85.38   9.259%   $93.2853   $93.29   $93.30   $93.30  
  Purchase #2 $202.42   10.515%   $223.7045   $223.70   $223.70   $223.70  
  Purchase #3 $150.49   8.196%   $162.8242   $162.82   $162.80   $162.80  
  Purchase #4 $47.76   6.437%   $50.8343   $50.83   $50.85   $50.80  
  Purchase #5 $208.56   8.719%   $226.7443   $226.74   $226.75   $226.70  
  Purchase #6 $42.30   7.498%   $45.4717   $45.47   $45.45   $45.50  
  Purchase #7 $122.30   6.270%   $129.9682   $129.97   $129.95   $130.00  
  7 purchase totals = $859.21       $932.8325   $932.82   $932.80   $932.80