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 $92.56   6.406%   $98.4894   $98.49   $98.50   $98.50  
  Purchase #2 $175.52   12.671%   $197.7601   $197.76   $197.75   $197.80  
  Purchase #3 $79.60   9.355%   $87.0466   $87.05   $87.05   $87.00  
  Purchase #4 $227.89   4.202%   $237.4659   $237.47   $237.45   $237.50  
  Purchase #5 $5.44   11.310%   $6.0553   $6.06   $6.05   $6.10  
  Purchase #6 $231.52   7.507%   $248.9002   $248.90   $248.90   $248.90  
  Purchase #7 $120.63   4.796%   $126.4154   $126.42   $126.40   $126.40  
  7 purchase totals = $933.16       $1,002.1329   $1,002.15   $1,002.10   $1,002.20