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 $68.68   12.439%   $77.2231   $77.22   $77.20   $77.20  
  Purchase #2 $193.94   11.643%   $216.5204   $216.52   $216.50   $216.50  
  Purchase #3 $111.44   5.130%   $117.1569   $117.16   $117.15   $117.20  
  Purchase #4 $186.51   9.266%   $203.792   $203.79   $203.80   $203.80  
  Purchase #5 $165.30   4.829%   $173.2823   $173.28   $173.30   $173.30  
  Purchase #6 $45.62   11.374%   $50.8088   $50.81   $50.80   $50.80  
  Purchase #7 $239.67   3.286%   $247.5456   $247.55   $247.55   $247.50  
  7 purchase totals = $1,011.16       $1,086.3291   $1,086.33   $1,086.30   $1,086.30