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 $93.56   5.313%   $98.5308   $98.53   $98.55   $98.50  
  Purchase #2 $230.39   3.584%   $238.6472   $238.65   $238.65   $238.60  
  Purchase #3 $225.96   5.319%   $237.9788   $237.98   $238.00   $238.00  
  Purchase #4 $183.44   5.540%   $193.6026   $193.60   $193.60   $193.60  
  Purchase #5 $26.33   11.698%   $29.4101   $29.41   $29.40   $29.40  
  Purchase #6 $200.25   3.579%   $207.4169   $207.42   $207.40   $207.40  
  Purchase #7 $134.90   11.836%   $150.8668   $150.87   $150.85   $150.90  
  7 purchase totals = $1,094.83       $1,156.4532   $1,156.46   $1,156.45   $1,156.40