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 $246.26   8.155%   $266.3425   $266.34   $266.35   $266.30  
  Purchase #2 $220.50   6.672%   $235.2118   $235.21   $235.20   $235.20  
  Purchase #3 $151.86   9.258%   $165.9192   $165.92   $165.90   $165.90  
  Purchase #4 $120.43   10.540%   $133.1233   $133.12   $133.10   $133.10  
  Purchase #5 $49.25   4.614%   $51.5224   $51.52   $51.50   $51.50  
  Purchase #6 $179.39   12.452%   $201.7276   $201.73   $201.75   $201.70  
  Purchase #7 $117.36   7.800%   $126.5141   $126.51   $126.50   $126.50  
  7 purchase totals = $1,085.05       $1,180.3609   $1,180.35   $1,180.30   $1,180.20