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 $227.74   11.618%   $254.1988   $254.20   $254.20   $254.20  
  Purchase #2 $208.64   12.612%   $234.9537   $234.95   $234.95   $235.00  
  Purchase #3 $39.26   8.729%   $42.687   $42.69   $42.70   $42.70  
  Purchase #4 $44.67   7.424%   $47.9863   $47.99   $48.00   $48.00  
  Purchase #5 $145.79   5.162%   $153.3157   $153.32   $153.30   $153.30  
  Purchase #6 $237.50   11.274%   $264.2758   $264.28   $264.30   $264.30  
  Purchase #7 $37.47   5.349%   $39.4743   $39.47   $39.45   $39.50  
  7 purchase totals = $941.07       $1,036.8916   $1,036.90   $1,036.90   $1,037.00