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 $59.98   4.688%   $62.7919   $62.79   $62.80   $62.80  
  Purchase #2 $10.66   8.286%   $11.5433   $11.54   $11.55   $11.50  
  Purchase #3 $126.26   3.198%   $130.2978   $130.30   $130.30   $130.30  
  Purchase #4 $230.31   6.701%   $245.7431   $245.74   $245.75   $245.70  
  Purchase #5 $87.71   7.820%   $94.5689   $94.57   $94.55   $94.60  
  Purchase #6 $215.60   8.437%   $233.7902   $233.79   $233.80   $233.80  
  Purchase #7 $37.32   4.221%   $38.8953   $38.90   $38.90   $38.90  
  7 purchase totals = $767.84       $817.6305   $817.63   $817.65   $817.60