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 $244.71   7.532%   $263.1416   $263.14   $263.15   $263.10  
  Purchase #2 $161.39   4.729%   $169.0221   $169.02   $169.00   $169.00  
  Purchase #3 $48.90   7.413%   $52.525   $52.53   $52.55   $52.50  
  Purchase #4 $174.54   6.461%   $185.817   $185.82   $185.80   $185.80  
  Purchase #5 $113.33   5.870%   $119.9825   $119.98   $120.00   $120.00  
  Purchase #6 $117.98   9.652%   $129.3674   $129.37   $129.35   $129.40  
  Purchase #7 $47.53   7.622%   $51.1527   $51.15   $51.15   $51.20  
  7 purchase totals = $908.38       $971.0083   $971.01   $971.00   $971.00