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 $110.63   7.166%   $118.5577   $118.56   $118.55   $118.60  
  Purchase #2 $248.49   5.766%   $262.8179   $262.82   $262.80   $262.80  
  Purchase #3 $48.76   13.626%   $55.404   $55.40   $55.40   $55.40  
  Purchase #4 $113.41   11.790%   $126.781   $126.78   $126.80   $126.80  
  Purchase #5 $98.69   12.364%   $110.892   $110.89   $110.90   $110.90  
  Purchase #6 $110.50   9.502%   $120.9997   $121.00   $121.00   $121.00  
  Purchase #7 $212.59   7.707%   $228.9743   $228.97   $228.95   $229.00  
  7 purchase totals = $943.07       $1,024.4266   $1,024.42   $1,024.40   $1,024.50