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 $61.55   7.664%   $66.2672   $66.27   $66.25   $66.30  
  Purchase #2 $110.57   12.623%   $124.5273   $124.53   $124.55   $124.50  
  Purchase #3 $152.47   12.731%   $171.881   $171.88   $171.90   $171.90  
  Purchase #4 $219.49   5.205%   $230.9145   $230.91   $230.90   $230.90  
  Purchase #5 $226.70   8.386%   $245.7111   $245.71   $245.70   $245.70  
  Purchase #6 $183.72   12.170%   $206.0787   $206.08   $206.10   $206.10  
  Purchase #7 $184.25   10.116%   $202.8887   $202.89   $202.90   $202.90  
  7 purchase totals = $1,138.75       $1,248.2685   $1,248.27   $1,248.30   $1,248.30