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 $58.60   10.266%   $64.6159   $64.62   $64.60   $64.60  
  Purchase #2 $149.45   8.791%   $162.5881   $162.59   $162.60   $162.60  
  Purchase #3 $62.80   11.255%   $69.8681   $69.87   $69.85   $69.90  
  Purchase #4 $137.72   8.529%   $149.4661   $149.47   $149.45   $149.50  
  Purchase #5 $159.77   3.487%   $165.3412   $165.34   $165.35   $165.30  
  Purchase #6 $121.34   3.301%   $125.3454   $125.35   $125.35   $125.30  
  Purchase #7 $108.90   5.694%   $115.1008   $115.10   $115.10   $115.10  
  7 purchase totals = $798.58       $852.3256   $852.34   $852.30   $852.30