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 $144.56   5.851%   $153.0182   $153.02   $153.00   $153.00  
  Purchase #2 $16.63   10.255%   $18.3354   $18.34   $18.35   $18.30  
  Purchase #3 $180.34   12.862%   $203.5353   $203.54   $203.55   $203.50  
  Purchase #4 $46.60   12.313%   $52.3379   $52.34   $52.35   $52.30  
  Purchase #5 $73.30   5.812%   $77.5602   $77.56   $77.55   $77.60  
  Purchase #6 $172.97   3.362%   $178.7853   $178.79   $178.80   $178.80  
  Purchase #7 $232.30   10.794%   $257.3745   $257.37   $257.35   $257.40  
  7 purchase totals = $866.70       $940.9468   $940.96   $940.95   $940.90