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 $222.29   6.483%   $236.7011   $236.70   $236.70   $236.70  
  Purchase #2 $106.54   10.249%   $117.4593   $117.46   $117.45   $117.50  
  Purchase #3 $82.60   13.110%   $93.4289   $93.43   $93.45   $93.40  
  Purchase #4 $205.87   5.298%   $216.777   $216.78   $216.80   $216.80  
  Purchase #5 $32.30   8.221%   $34.9554   $34.96   $34.95   $35.00  
  Purchase #6 $120.74   3.153%   $124.5469   $124.55   $124.55   $124.50  
  Purchase #7 $187.67   13.356%   $212.7352   $212.74   $212.75   $212.70  
  7 purchase totals = $958.01       $1,036.6038   $1,036.62   $1,036.65   $1,036.60