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 $58.43   13.831%   $66.5115   $66.51   $66.50   $66.50  
  Purchase #2 $226.83   3.736%   $235.3044   $235.30   $235.30   $235.30  
  Purchase #3 $168.79   11.784%   $188.6802   $188.68   $188.70   $188.70  
  Purchase #4 $140.66   6.815%   $150.246   $150.25   $150.25   $150.20  
  Purchase #5 $33.66   3.374%   $34.7957   $34.80   $34.80   $34.80  
  Purchase #6 $227.38   12.832%   $256.5574   $256.56   $256.55   $256.60  
  Purchase #7 $61.83   11.152%   $68.7253   $68.73   $68.75   $68.70  
  7 purchase totals = $917.58       $1,000.8205   $1,000.83   $1,000.85   $1,000.80