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 $84.53   10.328%   $93.2603   $93.26   $93.25   $93.30  
  Purchase #2 $94.32   3.471%   $97.5938   $97.59   $97.60   $97.60  
  Purchase #3 $51.85   5.135%   $54.5125   $54.51   $54.50   $54.50  
  Purchase #4 $229.84   8.172%   $248.6225   $248.62   $248.60   $248.60  
  Purchase #5 $207.76   12.141%   $232.9841   $232.98   $233.00   $233.00  
  Purchase #6 $55.35   5.206%   $58.2315   $58.23   $58.25   $58.20  
  Purchase #7 $228.64   10.707%   $253.1205   $253.12   $253.10   $253.10  
  7 purchase totals = $952.29       $1,038.3252   $1,038.31   $1,038.30   $1,038.30