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 $204.74   12.709%   $230.7604   $230.76   $230.75   $230.80  
  Purchase #2 $226.51   8.714%   $246.2481   $246.25   $246.25   $246.20  
  Purchase #3 $243.58   12.332%   $273.6183   $273.62   $273.60   $273.60  
  Purchase #4 $170.75   9.841%   $187.5535   $187.55   $187.55   $187.60  
  Purchase #5 $35.84   12.137%   $40.1899   $40.19   $40.20   $40.20  
  Purchase #6 $14.46   4.412%   $15.098   $15.10   $15.10   $15.10  
  Purchase #7 $66.49   11.417%   $74.0812   $74.08   $74.10   $74.10  
  7 purchase totals = $962.37       $1,067.5494   $1,067.55   $1,067.55   $1,067.60