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 $85.63   11.402%   $95.3935   $95.39   $95.40   $95.40  
  Purchase #2 $114.68   9.447%   $125.5138   $125.51   $125.50   $125.50  
  Purchase #3 $202.61   4.672%   $212.0759   $212.08   $212.10   $212.10  
  Purchase #4 $69.39   5.471%   $73.1863   $73.19   $73.20   $73.20  
  Purchase #5 $167.91   12.481%   $188.8668   $188.87   $188.85   $188.90  
  Purchase #6 $77.87   3.578%   $80.6562   $80.66   $80.65   $80.70  
  Purchase #7 $70.37   5.589%   $74.303   $74.30   $74.30   $74.30  
  7 purchase totals = $788.46       $849.9955   $850.00   $850.00   $850.10