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 $10.44   10.586%   $11.5452   $11.55   $11.55   $11.50  
  Purchase #2 $184.86   6.421%   $196.7299   $196.73   $196.75   $196.70  
  Purchase #3 $83.94   12.600%   $94.5164   $94.52   $94.50   $94.50  
  Purchase #4 $136.67   10.629%   $151.1967   $151.20   $151.20   $151.20  
  Purchase #5 $205.49   4.381%   $214.4925   $214.49   $214.50   $214.50  
  Purchase #6 $197.93   7.309%   $212.3967   $212.40   $212.40   $212.40  
  Purchase #7 $157.79   13.417%   $178.9607   $178.96   $178.95   $179.00  
  7 purchase totals = $977.12       $1,059.8381   $1,059.85   $1,059.85   $1,059.80