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 $82.53   7.723%   $88.9038   $88.90   $88.90   $88.90  
  Purchase #2 $56.49   8.381%   $61.2244   $61.22   $61.20   $61.20  
  Purchase #3 $238.28   3.408%   $246.4006   $246.40   $246.40   $246.40  
  Purchase #4 $104.40   11.272%   $116.168   $116.17   $116.15   $116.20  
  Purchase #5 $228.49   9.541%   $250.2902   $250.29   $250.30   $250.30  
  Purchase #6 $221.32   11.385%   $246.5173   $246.52   $246.50   $246.50  
  Purchase #7 $56.77   8.602%   $61.6534   $61.65   $61.65   $61.70  
  7 purchase totals = $988.28       $1,071.1577   $1,071.15   $1,071.10   $1,071.20