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 $42.75   4.608%   $44.7199   $44.72   $44.70   $44.70  
  Purchase #2 $244.65   9.424%   $267.7058   $267.71   $267.70   $267.70  
  Purchase #3 $204.31   4.428%   $213.3568   $213.36   $213.35   $213.40  
  Purchase #4 $213.39   6.263%   $226.7546   $226.75   $226.75   $226.80  
  Purchase #5 $53.88   12.207%   $60.4571   $60.46   $60.45   $60.50  
  Purchase #6 $246.68   13.564%   $280.1397   $280.14   $280.15   $280.10  
  Purchase #7 $196.36   4.184%   $204.5757   $204.58   $204.60   $204.60  
  7 purchase totals = $1,202.02       $1,297.7096   $1,297.72   $1,297.70   $1,297.80