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 $87.85   6.421%   $93.4908   $93.49   $93.50   $93.50  
  Purchase #2 $179.97   9.258%   $196.6316   $196.63   $196.65   $196.60  
  Purchase #3 $51.69   13.369%   $58.6004   $58.60   $58.60   $58.60  
  Purchase #4 $172.33   9.424%   $188.5704   $188.57   $188.55   $188.60  
  Purchase #5 $238.58   12.674%   $268.8176   $268.82   $268.80   $268.80  
  Purchase #6 $27.84   3.532%   $28.8233   $28.82   $28.80   $28.80  
  Purchase #7 $233.48   5.719%   $246.8327   $246.83   $246.85   $246.80  
  7 purchase totals = $991.74       $1,081.7668   $1,081.76   $1,081.75   $1,081.70