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 $247.96   10.192%   $273.2321   $273.23   $273.25   $273.20  
  Purchase #2 $100.92   5.483%   $106.4534   $106.45   $106.45   $106.50  
  Purchase #3 $189.55   7.778%   $204.2932   $204.29   $204.30   $204.30  
  Purchase #4 $203.33   3.544%   $210.536   $210.54   $210.55   $210.50  
  Purchase #5 $96.64   9.753%   $106.0653   $106.07   $106.05   $106.10  
  Purchase #6 $49.94   11.124%   $55.4953   $55.50   $55.50   $55.50  
  Purchase #7 $99.83   4.337%   $104.1596   $104.16   $104.15   $104.20  
  7 purchase totals = $988.17       $1,060.2349   $1,060.24   $1,060.25   $1,060.30