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 $221.70   11.741%   $247.7298   $247.73   $247.75   $247.70  
  Purchase #2 $67.51   13.763%   $76.8014   $76.80   $76.80   $76.80  
  Purchase #3 $222.29   13.344%   $251.9524   $251.95   $251.95   $252.00  
  Purchase #4 $69.40   4.661%   $72.6347   $72.63   $72.65   $72.60  
  Purchase #5 $128.81   4.469%   $134.5665   $134.57   $134.55   $134.60  
  Purchase #6 $219.39   4.156%   $228.5078   $228.51   $228.50   $228.50  
  Purchase #7 $68.93   5.270%   $72.5626   $72.56   $72.55   $72.60  
  7 purchase totals = $998.03       $1,084.7552   $1,084.75   $1,084.75   $1,084.80