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 $113.99   10.706%   $126.1938   $126.19   $126.20   $126.20  
  Purchase #2 $180.33   7.754%   $194.3128   $194.31   $194.30   $194.30  
  Purchase #3 $147.36   4.212%   $153.5668   $153.57   $153.55   $153.60  
  Purchase #4 $84.74   6.258%   $90.043   $90.04   $90.05   $90.00  
  Purchase #5 $194.46   3.817%   $201.8825   $201.88   $201.90   $201.90  
  Purchase #6 $182.86   12.354%   $205.4505   $205.45   $205.45   $205.50  
  Purchase #7 $28.68   11.119%   $31.8689   $31.87   $31.85   $31.90  
  7 purchase totals = $932.42       $1,003.3183   $1,003.31   $1,003.30   $1,003.40