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 $24.96   6.631%   $26.6151   $26.62   $26.60   $26.60  
  Purchase #2 $195.89   10.707%   $216.8639   $216.86   $216.85   $216.90  
  Purchase #3 $124.91   9.851%   $137.2149   $137.21   $137.20   $137.20  
  Purchase #4 $83.69   10.625%   $92.5821   $92.58   $92.60   $92.60  
  Purchase #5 $214.78   7.332%   $230.5277   $230.53   $230.55   $230.50  
  Purchase #6 $194.44   9.296%   $212.5151   $212.52   $212.50   $212.50  
  Purchase #7 $237.59   11.479%   $264.863   $264.86   $264.85   $264.90  
  7 purchase totals = $1,076.26       $1,181.1818   $1,181.18   $1,181.15   $1,181.20