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 $186.86   7.835%   $201.5005   $201.50   $201.50   $201.50  
  Purchase #2 $223.56   11.836%   $250.0206   $250.02   $250.00   $250.00  
  Purchase #3 $58.60   3.648%   $60.7377   $60.74   $60.75   $60.70  
  Purchase #4 $34.85   12.277%   $39.1285   $39.13   $39.15   $39.10  
  Purchase #5 $233.26   3.589%   $241.6317   $241.63   $241.65   $241.60  
  Purchase #6 $155.69   9.707%   $170.8028   $170.80   $170.80   $170.80  
  Purchase #7 $111.87   3.794%   $116.1143   $116.11   $116.10   $116.10  
  7 purchase totals = $1,004.69       $1,079.9361   $1,079.93   $1,079.95   $1,079.80