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 $158.52   10.231%   $174.7382   $174.74   $174.75   $174.70  
  Purchase #2 $76.32   11.154%   $84.8327   $84.83   $84.85   $84.80  
  Purchase #3 $76.39   5.663%   $80.716   $80.72   $80.70   $80.70  
  Purchase #4 $171.63   13.193%   $194.2731   $194.27   $194.25   $194.30  
  Purchase #5 $69.84   4.599%   $73.0519   $73.05   $73.05   $73.10  
  Purchase #6 $180.68   9.685%   $198.1789   $198.18   $198.20   $198.20  
  Purchase #7 $22.98   11.210%   $25.5561   $25.56   $25.55   $25.60  
  7 purchase totals = $756.36       $831.3469   $831.35   $831.35   $831.40