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 $50.32   9.201%   $54.9499   $54.95   $54.95   $54.90  
  Purchase #2 $176.52   4.643%   $184.7158   $184.72   $184.70   $184.70  
  Purchase #3 $199.34   6.288%   $211.8745   $211.87   $211.85   $211.90  
  Purchase #4 $209.61   5.220%   $220.5516   $220.55   $220.55   $220.60  
  Purchase #5 $179.35   8.120%   $193.9132   $193.91   $193.90   $193.90  
  Purchase #6 $86.35   8.370%   $93.5775   $93.58   $93.60   $93.60  
  Purchase #7 $220.43   9.198%   $240.7052   $240.71   $240.70   $240.70  
  7 purchase totals = $1,121.92       $1,200.2877   $1,200.29   $1,200.25   $1,200.30