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 $62.89   3.801%   $65.2804   $65.28   $65.30   $65.30  
  Purchase #2 $224.70   3.534%   $232.6409   $232.64   $232.65   $232.60  
  Purchase #3 $197.27   11.222%   $219.4076   $219.41   $219.40   $219.40  
  Purchase #4 $246.64   12.610%   $277.7413   $277.74   $277.75   $277.70  
  Purchase #5 $165.38   5.501%   $174.4776   $174.48   $174.50   $174.50  
  Purchase #6 $184.92   4.546%   $193.3265   $193.33   $193.35   $193.30  
  Purchase #7 $91.28   13.230%   $103.3563   $103.36   $103.35   $103.40  
  7 purchase totals = $1,173.08       $1,266.2306   $1,266.24   $1,266.30   $1,266.20