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 $246.63   8.665%   $268.0005   $268.00   $268.00   $268.00  
  Purchase #2 $33.54   12.248%   $37.648   $37.65   $37.65   $37.60  
  Purchase #3 $102.53   3.135%   $105.7443   $105.74   $105.75   $105.70  
  Purchase #4 $184.35   13.783%   $209.759   $209.76   $209.75   $209.80  
  Purchase #5 $88.54   8.221%   $95.8189   $95.82   $95.80   $95.80  
  Purchase #6 $212.34   8.502%   $230.3931   $230.39   $230.40   $230.40  
  Purchase #7 $163.57   13.403%   $185.4933   $185.49   $185.50   $185.50  
  7 purchase totals = $1,031.50       $1,132.8571   $1,132.85   $1,132.85   $1,132.80