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 $70.58   7.559%   $75.9151   $75.92   $75.90   $75.90  
  Purchase #2 $246.63   12.846%   $278.3121   $278.31   $278.30   $278.30  
  Purchase #3 $20.89   5.489%   $22.0367   $22.04   $22.05   $22.00  
  Purchase #4 $24.63   13.711%   $28.007   $28.01   $28.00   $28.00  
  Purchase #5 $223.82   7.809%   $241.2981   $241.30   $241.30   $241.30  
  Purchase #6 $81.36   13.750%   $92.547   $92.55   $92.55   $92.50  
  Purchase #7 $112.62   3.640%   $116.7194   $116.72   $116.70   $116.70  
  7 purchase totals = $780.53       $854.8354   $854.85   $854.80   $854.70