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 $64.56   5.434%   $68.0682   $68.07   $68.05   $68.10  
  Purchase #2 $221.41   4.668%   $231.7454   $231.75   $231.75   $231.70  
  Purchase #3 $10.75   5.291%   $11.3188   $11.32   $11.30   $11.30  
  Purchase #4 $204.49   5.631%   $216.0048   $216.00   $216.00   $216.00  
  Purchase #5 $75.25   5.251%   $79.2014   $79.20   $79.20   $79.20  
  Purchase #6 $55.34   9.516%   $60.6062   $60.61   $60.60   $60.60  
  Purchase #7 $134.52   3.521%   $139.2564   $139.26   $139.25   $139.30  
  7 purchase totals = $766.32       $806.2012   $806.21   $806.15   $806.20