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 $148.87   12.628%   $167.6693   $167.67   $167.65   $167.70  
  Purchase #2 $102.40   9.305%   $111.9283   $111.93   $111.95   $111.90  
  Purchase #3 $118.60   6.581%   $126.4051   $126.41   $126.40   $126.40  
  Purchase #4 $51.29   5.154%   $53.9335   $53.93   $53.95   $53.90  
  Purchase #5 $202.52   6.113%   $214.9   $214.90   $214.90   $214.90  
  Purchase #6 $93.84   8.341%   $101.6672   $101.67   $101.65   $101.70  
  Purchase #7 $104.31   12.357%   $117.1996   $117.20   $117.20   $117.20  
  7 purchase totals = $821.83       $893.7030   $893.71   $893.70   $893.70