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 $45.72   8.755%   $49.7228   $49.72   $49.70   $49.70  
  Purchase #2 $149.48   10.604%   $165.3309   $165.33   $165.35   $165.30  
  Purchase #3 $223.25   11.523%   $248.9751   $248.98   $249.00   $249.00  
  Purchase #4 $118.74   5.872%   $125.7124   $125.71   $125.70   $125.70  
  Purchase #5 $55.33   5.453%   $58.3471   $58.35   $58.35   $58.30  
  Purchase #6 $238.70   11.402%   $265.9166   $265.92   $265.90   $265.90  
  Purchase #7 $93.80   7.507%   $100.8416   $100.84   $100.85   $100.80  
  7 purchase totals = $925.02       $1,014.8465   $1,014.85   $1,014.85   $1,014.70