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 $223.51   13.567%   $253.8336   $253.83   $253.85   $253.80  
  Purchase #2 $159.52   9.612%   $174.8531   $174.85   $174.85   $174.90  
  Purchase #3 $44.76   9.753%   $49.1254   $49.13   $49.15   $49.10  
  Purchase #4 $88.57   6.747%   $94.5458   $94.55   $94.55   $94.50  
  Purchase #5 $246.57   7.761%   $265.7063   $265.71   $265.70   $265.70  
  Purchase #6 $88.42   13.393%   $100.2621   $100.26   $100.25   $100.30  
  Purchase #7 $112.49   11.811%   $125.7762   $125.78   $125.80   $125.80  
  7 purchase totals = $963.84       $1,064.1025   $1,064.11   $1,064.15   $1,064.10