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 $65.57   6.275%   $69.6845   $69.68   $69.70   $69.70  
  Purchase #2 $206.64   7.753%   $222.6608   $222.66   $222.65   $222.70  
  Purchase #3 $237.52   5.196%   $249.8615   $249.86   $249.85   $249.90  
  Purchase #4 $189.88   9.276%   $207.4933   $207.49   $207.50   $207.50  
  Purchase #5 $12.45   6.631%   $13.2756   $13.28   $13.30   $13.30  
  Purchase #6 $165.90   13.780%   $188.761   $188.76   $188.75   $188.80  
  Purchase #7 $206.97   13.390%   $234.6833   $234.68   $234.70   $234.70  
  7 purchase totals = $1,084.93       $1,186.4200   $1,186.41   $1,186.45   $1,186.60