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 $69.28   6.588%   $73.8442   $73.84   $73.85   $73.80  
  Purchase #2 $43.53   3.509%   $45.0575   $45.06   $45.05   $45.10  
  Purchase #3 $181.79   11.364%   $202.4486   $202.45   $202.45   $202.40  
  Purchase #4 $223.89   9.855%   $245.9544   $245.95   $245.95   $246.00  
  Purchase #5 $60.82   10.701%   $67.3283   $67.33   $67.35   $67.30  
  Purchase #6 $144.88   11.376%   $161.3615   $161.36   $161.35   $161.40  
  Purchase #7 $146.78   8.736%   $159.6027   $159.60   $159.60   $159.60  
  7 purchase totals = $870.97       $955.5972   $955.59   $955.60   $955.60