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 $131.36   3.244%   $135.6213   $135.62   $135.60   $135.60  
  Purchase #2 $128.89   8.461%   $139.7954   $139.80   $139.80   $139.80  
  Purchase #3 $200.47   10.235%   $220.9881   $220.99   $221.00   $221.00  
  Purchase #4 $165.26   3.606%   $171.2193   $171.22   $171.20   $171.20  
  Purchase #5 $148.77   12.840%   $167.8721   $167.87   $167.85   $167.90  
  Purchase #6 $55.39   13.697%   $62.9768   $62.98   $63.00   $63.00  
  Purchase #7 $83.87   6.245%   $89.1077   $89.11   $89.10   $89.10  
  7 purchase totals = $914.01       $987.5807   $987.59   $987.55   $987.60