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 $219.53   12.865%   $247.7725   $247.77   $247.75   $247.80  
  Purchase #2 $92.56   3.123%   $95.4506   $95.45   $95.45   $95.50  
  Purchase #3 $244.52   7.546%   $262.9715   $262.97   $262.95   $263.00  
  Purchase #4 $36.45   12.303%   $40.9344   $40.93   $40.95   $40.90  
  Purchase #5 $74.29   8.694%   $80.7488   $80.75   $80.75   $80.70  
  Purchase #6 $49.69   7.376%   $53.3551   $53.36   $53.35   $53.40  
  Purchase #7 $249.59   5.118%   $262.364   $262.36   $262.35   $262.40  
  7 purchase totals = $966.63       $1,043.5969   $1,043.59   $1,043.55   $1,043.70