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 $128.51   3.731%   $133.3047   $133.30   $133.30   $133.30  
  Purchase #2 $245.72   7.661%   $264.5446   $264.54   $264.55   $264.50  
  Purchase #3 $241.80   4.503%   $252.6883   $252.69   $252.70   $252.70  
  Purchase #4 $54.30   8.141%   $58.7206   $58.72   $58.70   $58.70  
  Purchase #5 $116.96   12.465%   $131.5391   $131.54   $131.55   $131.50  
  Purchase #6 $247.40   8.126%   $267.5037   $267.50   $267.50   $267.50  
  Purchase #7 $172.50   7.825%   $185.9981   $186.00   $186.00   $186.00  
  7 purchase totals = $1,207.19       $1,294.2991   $1,294.29   $1,294.30   $1,294.20