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 $110.96   13.559%   $126.0051   $126.01   $126.00   $126.00  
  Purchase #2 $144.51   10.598%   $159.8252   $159.83   $159.85   $159.80  
  Purchase #3 $171.38   10.413%   $189.2258   $189.23   $189.25   $189.20  
  Purchase #4 $179.26   8.357%   $194.2408   $194.24   $194.25   $194.20  
  Purchase #5 $60.64   5.726%   $64.1122   $64.11   $64.10   $64.10  
  Purchase #6 $135.80   6.768%   $144.9909   $144.99   $145.00   $145.00  
  Purchase #7 $162.44   5.779%   $171.8274   $171.83   $171.85   $171.80  
  7 purchase totals = $964.99       $1,050.2274   $1,050.24   $1,050.30   $1,050.10