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 $56.43   6.284%   $59.9761   $59.98   $60.00   $60.00  
  Purchase #2 $205.54   12.671%   $231.584   $231.58   $231.60   $231.60  
  Purchase #3 $83.26   4.179%   $86.7394   $86.74   $86.75   $86.70  
  Purchase #4 $206.52   10.282%   $227.7544   $227.75   $227.75   $227.80  
  Purchase #5 $68.34   5.265%   $71.9381   $71.94   $71.95   $71.90  
  Purchase #6 $75.44   12.158%   $84.612   $84.61   $84.60   $84.60  
  Purchase #7 $6.88   10.521%   $7.6038   $7.60   $7.60   $7.60  
  7 purchase totals = $702.41       $770.2078   $770.20   $770.25   $770.20