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 $86.56   11.508%   $96.5213   $96.52   $96.50   $96.50  
  Purchase #2 $220.99   7.624%   $237.8383   $237.84   $237.85   $237.80  
  Purchase #3 $246.62   6.513%   $262.6824   $262.68   $262.70   $262.70  
  Purchase #4 $39.25   10.700%   $43.4498   $43.45   $43.45   $43.40  
  Purchase #5 $153.47   3.787%   $159.2819   $159.28   $159.30   $159.30  
  Purchase #6 $8.57   12.282%   $9.6226   $9.62   $9.60   $9.60  
  Purchase #7 $229.84   10.201%   $253.286   $253.29   $253.30   $253.30  
  7 purchase totals = $985.30       $1,062.6823   $1,062.68   $1,062.70   $1,062.60