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 $60.54   6.150%   $64.2632   $64.26   $64.25   $64.30  
  Purchase #2 $137.29   5.569%   $144.9357   $144.94   $144.95   $144.90  
  Purchase #3 $199.52   6.624%   $212.7362   $212.74   $212.75   $212.70  
  Purchase #4 $222.81   7.659%   $239.875   $239.88   $239.90   $239.90  
  Purchase #5 $210.53   9.598%   $230.7367   $230.74   $230.75   $230.70  
  Purchase #6 $34.95   12.480%   $39.3118   $39.31   $39.30   $39.30  
  Purchase #7 $244.96   10.162%   $269.8528   $269.85   $269.85   $269.90  
  7 purchase totals = $1,110.60       $1,201.7114   $1,201.72   $1,201.75   $1,201.70