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 $197.52   7.761%   $212.8495   $212.85   $212.85   $212.80  
  Purchase #2 $24.77   3.232%   $25.5706   $25.57   $25.55   $25.60  
  Purchase #3 $208.49   13.236%   $236.0857   $236.09   $236.10   $236.10  
  Purchase #4 $91.57   10.836%   $101.4925   $101.49   $101.50   $101.50  
  Purchase #5 $53.82   7.310%   $57.7542   $57.75   $57.75   $57.80  
  Purchase #6 $164.78   3.664%   $170.8175   $170.82   $170.80   $170.80  
  Purchase #7 $159.41   4.433%   $166.4766   $166.48   $166.50   $166.50  
  7 purchase totals = $900.36       $971.0466   $971.05   $971.05   $971.10