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 $24.29   6.268%   $25.8125   $25.81   $25.80   $25.80  
  Purchase #2 $45.53   12.769%   $51.3437   $51.34   $51.35   $51.30  
  Purchase #3 $113.96   4.692%   $119.307   $119.31   $119.30   $119.30  
  Purchase #4 $19.91   3.408%   $20.5885   $20.59   $20.60   $20.60  
  Purchase #5 $171.58   11.645%   $191.5605   $191.56   $191.55   $191.60  
  Purchase #6 $181.81   6.110%   $192.9186   $192.92   $192.90   $192.90  
  Purchase #7 $188.70   4.673%   $197.518   $197.52   $197.50   $197.50  
  7 purchase totals = $745.78       $799.0488   $799.05   $799.00   $799.00