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 $60.36   9.310%   $65.9795   $65.98   $66.00   $66.00  
  Purchase #2 $160.53   12.254%   $180.2013   $180.20   $180.20   $180.20  
  Purchase #3 $247.32   8.580%   $268.5401   $268.54   $268.55   $268.50  
  Purchase #4 $130.65   5.365%   $137.6594   $137.66   $137.65   $137.70  
  Purchase #5 $51.55   3.377%   $53.2908   $53.29   $53.30   $53.30  
  Purchase #6 $205.75   6.422%   $218.9633   $218.96   $218.95   $219.00  
  Purchase #7 $30.35   5.275%   $31.951   $31.95   $31.95   $32.00  
  7 purchase totals = $886.51       $956.5854   $956.58   $956.60   $956.70