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 $46.28   6.758%   $49.4076   $49.41   $49.40   $49.40  
  Purchase #2 $38.62   13.827%   $43.96   $43.96   $43.95   $44.00  
  Purchase #3 $155.75   3.109%   $160.5923   $160.59   $160.60   $160.60  
  Purchase #4 $249.57   5.309%   $262.8197   $262.82   $262.80   $262.80  
  Purchase #5 $235.63   3.427%   $243.705   $243.71   $243.70   $243.70  
  Purchase #6 $189.32   11.844%   $211.7431   $211.74   $211.75   $211.70  
  Purchase #7 $29.39   10.131%   $32.3675   $32.37   $32.35   $32.40  
  7 purchase totals = $944.56       $1,004.5952   $1,004.60   $1,004.55   $1,004.60