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 $63.26   5.831%   $66.9487   $66.95   $66.95   $66.90  
  Purchase #2 $67.75   7.754%   $73.0033   $73.00   $73.00   $73.00  
  Purchase #3 $87.57   13.239%   $99.1634   $99.16   $99.15   $99.20  
  Purchase #4 $85.33   7.717%   $91.9149   $91.91   $91.90   $91.90  
  Purchase #5 $94.29   3.191%   $97.2988   $97.30   $97.30   $97.30  
  Purchase #6 $194.53   12.284%   $218.4261   $218.43   $218.45   $218.40  
  Purchase #7 $203.51   3.813%   $211.2698   $211.27   $211.25   $211.30  
  7 purchase totals = $796.24       $858.0250   $858.02   $858.00   $858.00