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 $165.65   8.207%   $179.2449   $179.24   $179.25   $179.20  
  Purchase #2 $108.29   6.142%   $114.9412   $114.94   $114.95   $114.90  
  Purchase #3 $54.95   7.654%   $59.1559   $59.16   $59.15   $59.20  
  Purchase #4 $18.57   5.284%   $19.5512   $19.55   $19.55   $19.60  
  Purchase #5 $98.25   8.836%   $106.9314   $106.93   $106.95   $106.90  
  Purchase #6 $193.86   9.457%   $212.1933   $212.19   $212.20   $212.20  
  Purchase #7 $79.94   5.332%   $84.2024   $84.20   $84.20   $84.20  
  7 purchase totals = $719.51       $776.2203   $776.21   $776.25   $776.20