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 $154.66   7.148%   $165.7151   $165.72   $165.70   $165.70  
  Purchase #2 $191.57   6.322%   $203.6811   $203.68   $203.70   $203.70  
  Purchase #3 $55.34   7.790%   $59.651   $59.65   $59.65   $59.70  
  Purchase #4 $63.37   9.837%   $69.6037   $69.60   $69.60   $69.60  
  Purchase #5 $113.61   8.759%   $123.5611   $123.56   $123.55   $123.60  
  Purchase #6 $67.84   13.347%   $76.8946   $76.89   $76.90   $76.90  
  Purchase #7 $61.29   3.461%   $63.4112   $63.41   $63.40   $63.40  
  7 purchase totals = $707.68       $762.5178   $762.51   $762.50   $762.60