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 $54.62   12.663%   $61.5365   $61.54   $61.55   $61.50  
  Purchase #2 $199.99   12.604%   $225.1967   $225.20   $225.20   $225.20  
  Purchase #3 $240.76   13.562%   $273.4119   $273.41   $273.40   $273.40  
  Purchase #4 $178.42   12.840%   $201.3291   $201.33   $201.35   $201.30  
  Purchase #5 $160.45   10.613%   $177.4786   $177.48   $177.50   $177.50  
  Purchase #6 $74.55   12.252%   $83.6839   $83.68   $83.70   $83.70  
  Purchase #7 $134.97   3.637%   $139.8789   $139.88   $139.90   $139.90  
  7 purchase totals = $1,043.76       $1,162.5156   $1,162.52   $1,162.60   $1,162.50