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 $148.45   8.573%   $161.1766   $161.18   $161.20   $161.20  
  Purchase #2 $174.38   3.709%   $180.8478   $180.85   $180.85   $180.80  
  Purchase #3 $41.36   7.651%   $44.5245   $44.52   $44.50   $44.50  
  Purchase #4 $211.56   9.282%   $231.197   $231.20   $231.20   $231.20  
  Purchase #5 $137.43   4.195%   $143.1952   $143.20   $143.20   $143.20  
  Purchase #6 $229.59   9.586%   $251.5985   $251.60   $251.60   $251.60  
  Purchase #7 $224.47   11.607%   $250.5242   $250.52   $250.50   $250.50  
  7 purchase totals = $1,167.24       $1,263.0638   $1,263.07   $1,263.05   $1,263.00