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 $171.53   13.127%   $194.0467   $194.05   $194.05   $194.00  
  Purchase #2 $55.77   12.436%   $62.7056   $62.71   $62.70   $62.70  
  Purchase #3 $93.34   9.803%   $102.4901   $102.49   $102.50   $102.50  
  Purchase #4 $198.72   3.460%   $205.5957   $205.60   $205.60   $205.60  
  Purchase #5 $75.92   6.672%   $80.9854   $80.99   $81.00   $81.00  
  Purchase #6 $128.43   8.565%   $139.43   $139.43   $139.45   $139.40  
  Purchase #7 $103.32   12.562%   $116.2991   $116.30   $116.30   $116.30  
  7 purchase totals = $827.03       $901.5526   $901.57   $901.60   $901.50