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 $7.74   4.534%   $8.0909   $8.09   $8.10   $8.10  
  Purchase #2 $123.52   7.206%   $132.4209   $132.42   $132.40   $132.40  
  Purchase #3 $243.52   10.434%   $268.9289   $268.93   $268.95   $268.90  
  Purchase #4 $96.41   3.736%   $100.0119   $100.01   $100.00   $100.00  
  Purchase #5 $187.75   4.357%   $195.9303   $195.93   $195.95   $195.90  
  Purchase #6 $65.49   9.391%   $71.6402   $71.64   $71.65   $71.60  
  Purchase #7 $89.47   7.798%   $96.4469   $96.45   $96.45   $96.40  
  7 purchase totals = $813.90       $873.4700   $873.47   $873.50   $873.30