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 $179.89   8.668%   $195.4829   $195.48   $195.50   $195.50  
  Purchase #2 $121.85   12.388%   $136.9448   $136.94   $136.95   $136.90  
  Purchase #3 $240.30   12.166%   $269.5349   $269.53   $269.55   $269.50  
  Purchase #4 $170.72   13.390%   $193.5794   $193.58   $193.60   $193.60  
  Purchase #5 $113.49   10.106%   $124.9593   $124.96   $124.95   $125.00  
  Purchase #6 $9.48   5.522%   $10.0035   $10.00   $10.00   $10.00  
  Purchase #7 $95.84   9.224%   $104.6803   $104.68   $104.70   $104.70  
  7 purchase totals = $931.57       $1,035.1851   $1,035.17   $1,035.25   $1,035.20