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 $183.55   11.151%   $204.0177   $204.02   $204.00   $204.00  
  Purchase #2 $47.32   13.475%   $53.6964   $53.70   $53.70   $53.70  
  Purchase #3 $103.72   6.603%   $110.5686   $110.57   $110.55   $110.60  
  Purchase #4 $184.37   11.443%   $205.4675   $205.47   $205.45   $205.50  
  Purchase #5 $34.71   4.684%   $36.3358   $36.34   $36.35   $36.30  
  Purchase #6 $61.77   6.477%   $65.7708   $65.77   $65.75   $65.80  
  Purchase #7 $173.92   7.270%   $186.564   $186.56   $186.55   $186.60  
  7 purchase totals = $789.36       $862.4208   $862.43   $862.35   $862.50