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 $45.81   13.317%   $51.9105   $51.91   $51.90   $51.90  
  Purchase #2 $229.32   13.813%   $260.996   $261.00   $261.00   $261.00  
  Purchase #3 $119.34   7.374%   $128.1401   $128.14   $128.15   $128.10  
  Purchase #4 $152.84   8.347%   $165.5976   $165.60   $165.60   $165.60  
  Purchase #5 $209.77   6.620%   $223.6568   $223.66   $223.65   $223.70  
  Purchase #6 $96.36   13.241%   $109.119   $109.12   $109.10   $109.10  
  Purchase #7 $113.75   6.568%   $121.2211   $121.22   $121.20   $121.20  
  7 purchase totals = $967.19       $1,060.6411   $1,060.65   $1,060.60   $1,060.60