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 $187.91   7.813%   $202.5914   $202.59   $202.60   $202.60  
  Purchase #2 $80.34   4.797%   $84.1939   $84.19   $84.20   $84.20  
  Purchase #3 $122.31   7.689%   $131.7144   $131.71   $131.70   $131.70  
  Purchase #4 $75.37   11.305%   $83.8906   $83.89   $83.90   $83.90  
  Purchase #5 $201.97   8.729%   $219.6   $219.60   $219.60   $219.60  
  Purchase #6 $159.55   10.130%   $175.7124   $175.71   $175.70   $175.70  
  Purchase #7 $246.85   5.315%   $259.9701   $259.97   $259.95   $260.00  
  7 purchase totals = $1,074.30       $1,157.6728   $1,157.66   $1,157.65   $1,157.70