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 $61.60   8.607%   $66.9019   $66.90   $66.90   $66.90  
  Purchase #2 $178.62   10.832%   $197.9681   $197.97   $197.95   $198.00  
  Purchase #3 $204.42   9.640%   $224.1261   $224.13   $224.15   $224.10  
  Purchase #4 $145.40   6.776%   $155.2523   $155.25   $155.25   $155.30  
  Purchase #5 $85.74   7.575%   $92.2348   $92.23   $92.25   $92.20  
  Purchase #6 $203.94   9.527%   $223.3694   $223.37   $223.35   $223.40  
  Purchase #7 $128.32   6.715%   $136.9367   $136.94   $136.95   $136.90  
  7 purchase totals = $1,008.04       $1,096.7893   $1,096.79   $1,096.80   $1,096.80