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 $83.34   5.144%   $87.627   $87.63   $87.65   $87.60  
  Purchase #2 $213.98   11.803%   $239.2361   $239.24   $239.25   $239.20  
  Purchase #3 $41.83   7.713%   $45.0563   $45.06   $45.05   $45.10  
  Purchase #4 $239.92   4.672%   $251.1291   $251.13   $251.15   $251.10  
  Purchase #5 $24.43   9.442%   $26.7367   $26.74   $26.75   $26.70  
  Purchase #6 $55.63   8.648%   $60.4409   $60.44   $60.45   $60.40  
  Purchase #7 $217.74   10.489%   $240.5787   $240.58   $240.60   $240.60  
  7 purchase totals = $876.87       $950.8048   $950.82   $950.90   $950.70