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 $211.53   6.859%   $226.0388   $226.04   $226.05   $226.00  
  Purchase #2 $174.55   13.783%   $198.6082   $198.61   $198.60   $198.60  
  Purchase #3 $201.55   11.398%   $224.5227   $224.52   $224.50   $224.50  
  Purchase #4 $82.62   4.157%   $86.0545   $86.05   $86.05   $86.10  
  Purchase #5 $67.80   9.250%   $74.0715   $74.07   $74.05   $74.10  
  Purchase #6 $94.46   10.813%   $104.674   $104.67   $104.65   $104.70  
  Purchase #7 $29.64   8.334%   $32.1102   $32.11   $32.10   $32.10  
  7 purchase totals = $862.15       $946.0799   $946.07   $946.00   $946.10