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 $61.88   6.550%   $65.9331   $65.93   $65.95   $65.90  
  Purchase #2 $135.35   9.394%   $148.0648   $148.06   $148.05   $148.10  
  Purchase #3 $115.51   10.168%   $127.2551   $127.26   $127.25   $127.30  
  Purchase #4 $53.37   9.729%   $58.5624   $58.56   $58.55   $58.60  
  Purchase #5 $202.82   6.598%   $216.2021   $216.20   $216.20   $216.20  
  Purchase #6 $25.43   8.548%   $27.6038   $27.60   $27.60   $27.60  
  Purchase #7 $177.54   9.310%   $194.069   $194.07   $194.05   $194.10  
  7 purchase totals = $771.90       $837.6903   $837.68   $837.65   $837.80