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 $194.64   8.517%   $211.2175   $211.22   $211.20   $211.20  
  Purchase #2 $148.83   4.377%   $155.3443   $155.34   $155.35   $155.30  
  Purchase #3 $34.49   6.449%   $36.7143   $36.71   $36.70   $36.70  
  Purchase #4 $199.94   7.549%   $215.0335   $215.03   $215.05   $215.00  
  Purchase #5 $78.67   12.686%   $88.6501   $88.65   $88.65   $88.70  
  Purchase #6 $206.32   8.414%   $223.6798   $223.68   $223.70   $223.70  
  Purchase #7 $87.47   6.619%   $93.2596   $93.26   $93.25   $93.30  
  7 purchase totals = $950.36       $1,023.8991   $1,023.89   $1,023.90   $1,023.90