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 $117.98   5.363%   $124.3073   $124.31   $124.30   $124.30  
  Purchase #2 $221.58   8.836%   $241.1588   $241.16   $241.15   $241.20  
  Purchase #3 $118.95   11.133%   $132.1927   $132.19   $132.20   $132.20  
  Purchase #4 $193.33   9.603%   $211.8955   $211.90   $211.90   $211.90  
  Purchase #5 $26.63   8.721%   $28.9524   $28.95   $28.95   $29.00  
  Purchase #6 $207.42   9.691%   $227.5211   $227.52   $227.50   $227.50  
  Purchase #7 $150.81   13.802%   $171.6248   $171.62   $171.60   $171.60  
  7 purchase totals = $1,036.70       $1,137.6526   $1,137.65   $1,137.60   $1,137.70