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 $244.62   7.530%   $263.0399   $263.04   $263.05   $263.00  
  Purchase #2 $83.66   8.290%   $90.5954   $90.60   $90.60   $90.60  
  Purchase #3 $65.87   11.288%   $73.3054   $73.31   $73.30   $73.30  
  Purchase #4 $62.99   12.313%   $70.746   $70.75   $70.75   $70.70  
  Purchase #5 $229.37   11.819%   $256.4792   $256.48   $256.50   $256.50  
  Purchase #6 $10.33   8.656%   $11.2242   $11.22   $11.20   $11.20  
  Purchase #7 $54.30   4.221%   $56.592   $56.59   $56.60   $56.60  
  7 purchase totals = $751.14       $821.9821   $821.99   $822.00   $821.90