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 $50.27   13.284%   $56.9479   $56.95   $56.95   $56.90  
  Purchase #2 $202.31   10.382%   $223.3138   $223.31   $223.30   $223.30  
  Purchase #3 $229.81   10.604%   $254.1791   $254.18   $254.20   $254.20  
  Purchase #4 $147.87   3.592%   $153.1815   $153.18   $153.20   $153.20  
  Purchase #5 $237.88   7.664%   $256.1111   $256.11   $256.10   $256.10  
  Purchase #6 $121.31   12.803%   $136.8413   $136.84   $136.85   $136.80  
  Purchase #7 $176.36   4.330%   $183.9964   $184.00   $184.00   $184.00  
  7 purchase totals = $1,165.81       $1,264.5711   $1,264.57   $1,264.60   $1,264.50