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 $160.41   6.770%   $171.2698   $171.27   $171.25   $171.30  
  Purchase #2 $235.71   11.298%   $262.3405   $262.34   $262.35   $262.30  
  Purchase #3 $112.97   13.772%   $128.5282   $128.53   $128.55   $128.50  
  Purchase #4 $167.78   4.776%   $175.7932   $175.79   $175.80   $175.80  
  Purchase #5 $160.31   8.673%   $174.2137   $174.21   $174.20   $174.20  
  Purchase #6 $22.29   7.580%   $23.9796   $23.98   $24.00   $24.00  
  Purchase #7 $62.69   3.232%   $64.7161   $64.72   $64.70   $64.70  
  7 purchase totals = $922.16       $1,000.8411   $1,000.84   $1,000.85   $1,000.80