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 $23.51   6.373%   $25.0083   $25.01   $25.00   $25.00  
  Purchase #2 $159.38   3.722%   $165.3121   $165.31   $165.30   $165.30  
  Purchase #3 $68.90   6.393%   $73.3048   $73.30   $73.30   $73.30  
  Purchase #4 $146.26   4.610%   $153.0026   $153.00   $153.00   $153.00  
  Purchase #5 $230.83   11.315%   $256.9484   $256.95   $256.95   $256.90  
  Purchase #6 $77.31   9.103%   $84.3475   $84.35   $84.35   $84.30  
  Purchase #7 $39.31   11.172%   $43.7017   $43.70   $43.70   $43.70  
  7 purchase totals = $745.50       $801.6254   $801.62   $801.60   $801.50