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 $204.78   4.652%   $214.3064   $214.31   $214.30   $214.30  
  Purchase #2 $160.25   3.441%   $165.7642   $165.76   $165.75   $165.80  
  Purchase #3 $97.54   13.437%   $110.6464   $110.65   $110.65   $110.60  
  Purchase #4 $64.98   10.354%   $71.708   $71.71   $71.70   $71.70  
  Purchase #5 $184.89   4.747%   $193.6667   $193.67   $193.65   $193.70  
  Purchase #6 $231.91   5.522%   $244.7161   $244.72   $244.70   $244.70  
  Purchase #7 $236.99   11.333%   $263.8481   $263.85   $263.85   $263.80  
  7 purchase totals = $1,181.34       $1,264.6559   $1,264.67   $1,264.60   $1,264.60