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 $86.61   5.446%   $91.3268   $91.33   $91.35   $91.30  
  Purchase #2 $220.98   7.408%   $237.3502   $237.35   $237.35   $237.40  
  Purchase #3 $40.81   4.432%   $42.6187   $42.62   $42.60   $42.60  
  Purchase #4 $212.55   7.240%   $227.9386   $227.94   $227.95   $227.90  
  Purchase #5 $173.88   3.752%   $180.404   $180.40   $180.40   $180.40  
  Purchase #6 $209.44   11.249%   $232.9999   $233.00   $233.00   $233.00  
  Purchase #7 $17.27   5.476%   $18.2157   $18.22   $18.20   $18.20  
  7 purchase totals = $961.54       $1,030.8539   $1,030.86   $1,030.85   $1,030.80