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 $91.98   5.745%   $97.2643   $97.26   $97.25   $97.30  
  Purchase #2 $183.29   3.316%   $189.3679   $189.37   $189.35   $189.40  
  Purchase #3 $234.90   12.306%   $263.8068   $263.81   $263.80   $263.80  
  Purchase #4 $17.96   9.795%   $19.7192   $19.72   $19.70   $19.70  
  Purchase #5 $190.75   5.784%   $201.783   $201.78   $201.80   $201.80  
  Purchase #6 $35.92   4.165%   $37.4161   $37.42   $37.40   $37.40  
  Purchase #7 $198.33   3.632%   $205.5333   $205.53   $205.55   $205.50  
  7 purchase totals = $953.13       $1,014.8906   $1,014.89   $1,014.85   $1,014.90