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 $57.92   3.519%   $59.9582   $59.96   $59.95   $60.00  
  Purchase #2 $15.26   8.652%   $16.5803   $16.58   $16.60   $16.60  
  Purchase #3 $109.71   8.600%   $119.1451   $119.15   $119.15   $119.10  
  Purchase #4 $238.89   12.380%   $268.4646   $268.46   $268.45   $268.50  
  Purchase #5 $237.70   8.396%   $257.6573   $257.66   $257.65   $257.70  
  Purchase #6 $209.61   10.137%   $230.8582   $230.86   $230.85   $230.90  
  Purchase #7 $187.75   8.613%   $203.9209   $203.92   $203.90   $203.90  
  7 purchase totals = $1,056.84       $1,156.5846   $1,156.59   $1,156.55   $1,156.70