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 $86.38   11.745%   $96.5253   $96.53   $96.55   $96.50  
  Purchase #2 $226.51   3.287%   $233.9554   $233.96   $233.95   $234.00  
  Purchase #3 $131.31   7.631%   $141.3303   $141.33   $141.35   $141.30  
  Purchase #4 $241.36   4.219%   $251.543   $251.54   $251.55   $251.50  
  Purchase #5 $102.97   9.855%   $113.1177   $113.12   $113.10   $113.10  
  Purchase #6 $67.40   6.376%   $71.6974   $71.70   $71.70   $71.70  
  Purchase #7 $140.84   3.740%   $146.1074   $146.11   $146.10   $146.10  
  7 purchase totals = $996.77       $1,054.2765   $1,054.29   $1,054.30   $1,054.20