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 $106.27   12.316%   $119.3582   $119.36   $119.35   $119.40  
  Purchase #2 $220.80   5.774%   $233.549   $233.55   $233.55   $233.50  
  Purchase #3 $104.76   12.677%   $118.0404   $118.04   $118.05   $118.00  
  Purchase #4 $201.56   10.107%   $221.9317   $221.93   $221.95   $221.90  
  Purchase #5 $62.26   9.831%   $68.3808   $68.38   $68.40   $68.40  
  Purchase #6 $174.91   10.606%   $193.461   $193.46   $193.45   $193.50  
  Purchase #7 $82.90   9.503%   $90.778   $90.78   $90.80   $90.80  
  7 purchase totals = $953.46       $1,045.4991   $1,045.50   $1,045.55   $1,045.50