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 $45.62   7.511%   $49.0465   $49.05   $49.05   $49.00  
  Purchase #2 $41.68   7.351%   $44.7439   $44.74   $44.75   $44.70  
  Purchase #3 $69.66   4.758%   $72.9744   $72.97   $72.95   $73.00  
  Purchase #4 $61.78   9.802%   $67.8357   $67.84   $67.85   $67.80  
  Purchase #5 $36.76   4.145%   $38.2837   $38.28   $38.30   $38.30  
  Purchase #6 $8.68   7.104%   $9.2966   $9.30   $9.30   $9.30  
  Purchase #7 $12.95   6.710%   $13.8189   $13.82   $13.80   $13.80  
  7 purchase totals = $277.13       $295.9997   $296.00   $296.00   $295.90