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 $84.49   10.751%   $93.5735   $93.57   $93.55   $93.60  
  Purchase #2 $224.60   9.833%   $246.6849   $246.68   $246.70   $246.70  
  Purchase #3 $197.83   12.844%   $223.2393   $223.24   $223.25   $223.20  
  Purchase #4 $119.94   13.306%   $135.8992   $135.90   $135.90   $135.90  
  Purchase #5 $80.67   9.277%   $88.1538   $88.15   $88.15   $88.20  
  Purchase #6 $31.30   6.424%   $33.3107   $33.31   $33.30   $33.30  
  Purchase #7 $75.92   13.812%   $86.4061   $86.41   $86.40   $86.40  
  7 purchase totals = $814.75       $907.2675   $907.26   $907.25   $907.30