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 $5.34   3.238%   $5.5129   $5.51   $5.50   $5.50  
  Purchase #2 $235.59   10.681%   $260.7534   $260.75   $260.75   $260.80  
  Purchase #3 $59.96   11.119%   $66.627   $66.63   $66.65   $66.60  
  Purchase #4 $163.67   10.345%   $180.6017   $180.60   $180.60   $180.60  
  Purchase #5 $201.40   5.568%   $212.614   $212.61   $212.60   $212.60  
  Purchase #6 $185.58   13.331%   $210.3197   $210.32   $210.30   $210.30  
  Purchase #7 $135.26   3.579%   $140.101   $140.10   $140.10   $140.10  
  7 purchase totals = $986.80       $1,076.5297   $1,076.52   $1,076.50   $1,076.50