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 $171.82   13.252%   $194.5896   $194.59   $194.60   $194.60  
  Purchase #2 $236.65   9.647%   $259.4796   $259.48   $259.50   $259.50  
  Purchase #3 $244.47   12.131%   $274.1267   $274.13   $274.15   $274.10  
  Purchase #4 $88.40   9.144%   $96.4833   $96.48   $96.50   $96.50  
  Purchase #5 $44.76   11.399%   $49.8622   $49.86   $49.85   $49.90  
  Purchase #6 $124.76   8.343%   $135.1687   $135.17   $135.15   $135.20  
  Purchase #7 $134.98   4.323%   $140.8152   $140.82   $140.80   $140.80  
  7 purchase totals = $1,045.84       $1,150.5253   $1,150.53   $1,150.55   $1,150.60