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 $32.66   11.268%   $36.3401   $36.34   $36.35   $36.30  
  Purchase #2 $59.25   4.122%   $61.6923   $61.69   $61.70   $61.70  
  Purchase #3 $46.56   8.576%   $50.553   $50.55   $50.55   $50.60  
  Purchase #4 $74.78   11.749%   $83.5659   $83.57   $83.55   $83.60  
  Purchase #5 $146.41   13.323%   $165.9162   $165.92   $165.90   $165.90  
  Purchase #6 $133.63   5.361%   $140.7939   $140.79   $140.80   $140.80  
  Purchase #7 $128.31   4.416%   $133.9762   $133.98   $134.00   $134.00  
  7 purchase totals = $621.60       $672.8376   $672.84   $672.85   $672.90