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 $144.27   12.717%   $162.6168   $162.62   $162.60   $162.60  
  Purchase #2 $89.38   4.200%   $93.134   $93.13   $93.15   $93.10  
  Purchase #3 $61.87   8.793%   $67.3102   $67.31   $67.30   $67.30  
  Purchase #4 $234.74   6.765%   $250.6202   $250.62   $250.60   $250.60  
  Purchase #5 $200.60   13.131%   $226.9408   $226.94   $226.95   $226.90  
  Purchase #6 $110.99   5.581%   $117.1844   $117.18   $117.20   $117.20  
  Purchase #7 $110.79   6.197%   $117.6557   $117.66   $117.65   $117.70  
  7 purchase totals = $952.64       $1,035.4621   $1,035.46   $1,035.45   $1,035.40