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 $59.84   13.590%   $67.9723   $67.97   $67.95   $68.00  
  Purchase #2 $178.82   9.801%   $196.3461   $196.35   $196.35   $196.30  
  Purchase #3 $36.53   13.728%   $41.5448   $41.54   $41.55   $41.50  
  Purchase #4 $7.31   9.679%   $8.0175   $8.02   $8.00   $8.00  
  Purchase #5 $24.71   12.763%   $27.8637   $27.86   $27.85   $27.90  
  Purchase #6 $246.45   12.809%   $278.0178   $278.02   $278.00   $278.00  
  Purchase #7 $123.60   11.697%   $138.0575   $138.06   $138.05   $138.10  
  7 purchase totals = $677.26       $757.8197   $757.82   $757.75   $757.80