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 $6.98   9.850%   $7.6675   $7.67   $7.65   $7.70  
  Purchase #2 $89.88   9.151%   $98.1049   $98.10   $98.10   $98.10  
  Purchase #3 $76.41   5.278%   $80.4429   $80.44   $80.45   $80.40  
  Purchase #4 $170.68   5.127%   $179.4308   $179.43   $179.45   $179.40  
  Purchase #5 $189.37   11.658%   $211.4468   $211.45   $211.45   $211.40  
  Purchase #6 $110.32   9.337%   $120.6206   $120.62   $120.60   $120.60  
  Purchase #7 $164.96   10.419%   $182.1472   $182.15   $182.15   $182.10  
  7 purchase totals = $808.60       $879.8607   $879.86   $879.85   $879.70