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 $218.95   12.592%   $246.5202   $246.52   $246.50   $246.50  
  Purchase #2 $44.87   7.176%   $48.0899   $48.09   $48.10   $48.10  
  Purchase #3 $70.53   5.498%   $74.4077   $74.41   $74.40   $74.40  
  Purchase #4 $190.96   8.585%   $207.3539   $207.35   $207.35   $207.40  
  Purchase #5 $68.73   11.433%   $76.5879   $76.59   $76.60   $76.60  
  Purchase #6 $232.61   9.866%   $255.5593   $255.56   $255.55   $255.60  
  Purchase #7 $160.53   6.361%   $170.7413   $170.74   $170.75   $170.70  
  7 purchase totals = $987.18       $1,079.2602   $1,079.26   $1,079.25   $1,079.30