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 $220.86   11.459%   $246.1683   $246.17   $246.15   $246.20  
  Purchase #2 $98.69   10.681%   $109.2311   $109.23   $109.25   $109.20  
  Purchase #3 $87.47   4.719%   $91.5977   $91.60   $91.60   $91.60  
  Purchase #4 $230.58   10.448%   $254.671   $254.67   $254.65   $254.70  
  Purchase #5 $68.74   10.349%   $75.8539   $75.85   $75.85   $75.90  
  Purchase #6 $169.32   5.488%   $178.6123   $178.61   $178.60   $178.60  
  Purchase #7 $11.30   13.734%   $12.8519   $12.85   $12.85   $12.90  
  7 purchase totals = $886.96       $968.9862   $968.98   $968.95   $969.10