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 $91.60   5.762%   $96.878   $96.88   $96.90   $96.90  
  Purchase #2 $219.34   9.376%   $239.9053   $239.91   $239.90   $239.90  
  Purchase #3 $43.70   4.395%   $45.6206   $45.62   $45.60   $45.60  
  Purchase #4 $200.76   9.848%   $220.5308   $220.53   $220.55   $220.50  
  Purchase #5 $72.76   5.630%   $76.8564   $76.86   $76.85   $76.90  
  Purchase #6 $97.72   13.405%   $110.8194   $110.82   $110.80   $110.80  
  Purchase #7 $132.96   12.348%   $149.3779   $149.38   $149.40   $149.40  
  7 purchase totals = $858.84       $939.9884   $940.00   $940.00   $940.00