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 $212.62   13.617%   $241.5725   $241.57   $241.55   $241.60  
  Purchase #2 $225.64   11.836%   $252.3468   $252.35   $252.35   $252.30  
  Purchase #3 $113.85   7.688%   $122.6028   $122.60   $122.60   $122.60  
  Purchase #4 $6.86   7.107%   $7.3475   $7.35   $7.35   $7.30  
  Purchase #5 $28.38   3.196%   $29.287   $29.29   $29.30   $29.30  
  Purchase #6 $210.78   7.159%   $225.8697   $225.87   $225.85   $225.90  
  Purchase #7 $10.26   6.823%   $10.96   $10.96   $10.95   $11.00  
  7 purchase totals = $808.39       $889.9863   $889.99   $889.95   $890.00