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 $125.53   9.817%   $137.8533   $137.85   $137.85   $137.90  
  Purchase #2 $181.30   12.154%   $203.3352   $203.34   $203.35   $203.30  
  Purchase #3 $171.32   9.731%   $187.9911   $187.99   $188.00   $188.00  
  Purchase #4 $96.90   8.256%   $104.9001   $104.90   $104.90   $104.90  
  Purchase #5 $119.85   13.176%   $135.6414   $135.64   $135.65   $135.60  
  Purchase #6 $53.54   4.870%   $56.1474   $56.15   $56.15   $56.10  
  Purchase #7 $170.58   8.405%   $184.9172   $184.92   $184.90   $184.90  
  7 purchase totals = $919.02       $1,010.7857   $1,010.79   $1,010.80   $1,010.70