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 $192.35   6.819%   $205.4663   $205.47   $205.45   $205.50  
  Purchase #2 $88.77   6.846%   $94.8472   $94.85   $94.85   $94.80  
  Purchase #3 $216.33   4.287%   $225.6041   $225.60   $225.60   $225.60  
  Purchase #4 $51.37   8.176%   $55.57   $55.57   $55.55   $55.60  
  Purchase #5 $250.60   11.829%   $280.2435   $280.24   $280.25   $280.20  
  Purchase #6 $147.74   7.700%   $159.116   $159.12   $159.10   $159.10  
  Purchase #7 $77.81   12.418%   $87.4724   $87.47   $87.45   $87.50  
  7 purchase totals = $1,024.97       $1,108.3195   $1,108.32   $1,108.25   $1,108.30