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 $223.93   12.819%   $252.6356   $252.64   $252.65   $252.60  
  Purchase #2 $245.79   9.398%   $268.8893   $268.89   $268.90   $268.90  
  Purchase #3 $188.90   13.424%   $214.2579   $214.26   $214.25   $214.30  
  Purchase #4 $77.76   12.272%   $87.3027   $87.30   $87.30   $87.30  
  Purchase #5 $102.89   3.743%   $106.7412   $106.74   $106.75   $106.70  
  Purchase #6 $180.83   11.331%   $201.3198   $201.32   $201.30   $201.30  
  Purchase #7 $247.64   10.153%   $272.7829   $272.78   $272.80   $272.80  
  7 purchase totals = $1,267.74       $1,403.9294   $1,403.93   $1,403.95   $1,403.90