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 $206.77   7.402%   $222.0751   $222.08   $222.10   $222.10  
  Purchase #2 $95.39   7.261%   $102.3163   $102.32   $102.30   $102.30  
  Purchase #3 $61.38   10.309%   $67.7077   $67.71   $67.70   $67.70  
  Purchase #4 $193.93   6.674%   $206.8729   $206.87   $206.85   $206.90  
  Purchase #5 $190.51   5.330%   $200.6642   $200.66   $200.65   $200.70  
  Purchase #6 $178.45   13.615%   $202.746   $202.75   $202.75   $202.70  
  Purchase #7 $9.40   11.813%   $10.5104   $10.51   $10.50   $10.50  
  7 purchase totals = $935.83       $1,012.8926   $1,012.90   $1,012.85   $1,012.90