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 $34.40   8.423%   $37.2975   $37.30   $37.30   $37.30  
  Purchase #2 $119.67   13.632%   $135.9834   $135.98   $136.00   $136.00  
  Purchase #3 $188.81   3.830%   $196.0414   $196.04   $196.05   $196.00  
  Purchase #4 $147.42   4.370%   $153.8623   $153.86   $153.85   $153.90  
  Purchase #5 $8.71   6.614%   $9.2861   $9.29   $9.30   $9.30  
  Purchase #6 $58.69   12.447%   $65.9951   $66.00   $66.00   $66.00  
  Purchase #7 $152.65   9.264%   $166.7915   $166.79   $166.80   $166.80  
  7 purchase totals = $710.35       $765.2573   $765.26   $765.30   $765.30