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 $229.80   7.775%   $247.667   $247.67   $247.65   $247.70  
  Purchase #2 $66.35   12.761%   $74.8169   $74.82   $74.80   $74.80  
  Purchase #3 $241.95   7.267%   $259.5325   $259.53   $259.55   $259.50  
  Purchase #4 $209.27   7.363%   $224.6786   $224.68   $224.70   $224.70  
  Purchase #5 $99.85   9.710%   $109.5454   $109.55   $109.55   $109.50  
  Purchase #6 $60.49   12.301%   $67.9309   $67.93   $67.95   $67.90  
  Purchase #7 $163.82   10.676%   $181.3094   $181.31   $181.30   $181.30  
  7 purchase totals = $1,071.53       $1,165.4807   $1,165.49   $1,165.50   $1,165.40