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 $72.35   5.511%   $76.3372   $76.34   $76.35   $76.30  
  Purchase #2 $226.50   10.426%   $250.1149   $250.11   $250.10   $250.10  
  Purchase #3 $207.63   12.440%   $233.4592   $233.46   $233.45   $233.50  
  Purchase #4 $212.90   12.395%   $239.289   $239.29   $239.30   $239.30  
  Purchase #5 $49.59   10.550%   $54.8217   $54.82   $54.80   $54.80  
  Purchase #6 $120.74   9.311%   $131.9821   $131.98   $132.00   $132.00  
  Purchase #7 $25.90   7.169%   $27.7568   $27.76   $27.75   $27.80  
  7 purchase totals = $915.61       $1,013.7609   $1,013.76   $1,013.75   $1,013.80