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 $64.78   5.676%   $68.4569   $68.46   $68.45   $68.50  
  Purchase #2 $200.42   6.212%   $212.8701   $212.87   $212.85   $212.90  
  Purchase #3 $12.33   5.177%   $12.9683   $12.97   $12.95   $13.00  
  Purchase #4 $181.62   5.722%   $192.0123   $192.01   $192.00   $192.00  
  Purchase #5 $159.43   8.802%   $173.463   $173.46   $173.45   $173.50  
  Purchase #6 $240.55   11.351%   $267.8548   $267.85   $267.85   $267.90  
  Purchase #7 $97.62   7.162%   $104.6115   $104.61   $104.60   $104.60  
  7 purchase totals = $956.75       $1,032.2369   $1,032.23   $1,032.15   $1,032.40