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 $54.95   10.760%   $60.8626   $60.86   $60.85   $60.90  
  Purchase #2 $189.91   6.232%   $201.7452   $201.75   $201.75   $201.70  
  Purchase #3 $231.43   11.854%   $258.8637   $258.86   $258.85   $258.90  
  Purchase #4 $98.78   13.550%   $112.1647   $112.16   $112.15   $112.20  
  Purchase #5 $135.47   11.163%   $150.5925   $150.59   $150.60   $150.60  
  Purchase #6 $120.31   11.856%   $134.574   $134.57   $134.55   $134.60  
  Purchase #7 $51.55   9.791%   $56.5973   $56.60   $56.60   $56.60  
  7 purchase totals = $882.40       $975.4000   $975.39   $975.35   $975.50