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 $201.62   4.710%   $211.1163   $211.12   $211.10   $211.10  
  Purchase #2 $52.64   13.376%   $59.6811   $59.68   $59.70   $59.70  
  Purchase #3 $205.27   12.561%   $231.054   $231.05   $231.05   $231.10  
  Purchase #4 $36.55   10.566%   $40.4119   $40.41   $40.40   $40.40  
  Purchase #5 $15.29   11.306%   $17.0187   $17.02   $17.00   $17.00  
  Purchase #6 $208.33   13.722%   $236.917   $236.92   $236.90   $236.90  
  Purchase #7 $67.98   6.126%   $72.1445   $72.14   $72.15   $72.10  
  7 purchase totals = $787.68       $868.3435   $868.34   $868.30   $868.30