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 $248.35   9.697%   $272.4325   $272.43   $272.45   $272.40  
  Purchase #2 $199.97   6.331%   $212.6301   $212.63   $212.65   $212.60  
  Purchase #3 $221.53   7.113%   $237.2874   $237.29   $237.30   $237.30  
  Purchase #4 $65.45   9.728%   $71.817   $71.82   $71.80   $71.80  
  Purchase #5 $144.81   11.176%   $160.994   $160.99   $161.00   $161.00  
  Purchase #6 $152.55   9.534%   $167.0941   $167.09   $167.10   $167.10  
  Purchase #7 $41.94   5.738%   $44.3465   $44.35   $44.35   $44.30  
  7 purchase totals = $1,074.60       $1,166.6016   $1,166.60   $1,166.65   $1,166.50