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 $245.91   11.443%   $274.0495   $274.05   $274.05   $274.00  
  Purchase #2 $46.46   4.396%   $48.5024   $48.50   $48.50   $48.50  
  Purchase #3 $148.60   7.296%   $159.4419   $159.44   $159.45   $159.40  
  Purchase #4 $203.73   10.337%   $224.7896   $224.79   $224.80   $224.80  
  Purchase #5 $155.25   13.140%   $175.6499   $175.65   $175.65   $175.60  
  Purchase #6 $61.31   11.771%   $68.5268   $68.53   $68.55   $68.50  
  Purchase #7 $104.93   4.405%   $109.5522   $109.55   $109.55   $109.60  
  7 purchase totals = $966.19       $1,060.5123   $1,060.51   $1,060.55   $1,060.40