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 $250.95   9.247%   $274.1553   $274.16   $274.15   $274.20  
  Purchase #2 $158.67   11.809%   $177.4073   $177.41   $177.40   $177.40  
  Purchase #3 $139.41   13.232%   $157.8567   $157.86   $157.85   $157.90  
  Purchase #4 $96.85   10.324%   $106.8488   $106.85   $106.85   $106.80  
  Purchase #5 $22.57   10.563%   $24.9541   $24.95   $24.95   $25.00  
  Purchase #6 $141.36   10.126%   $155.6741   $155.67   $155.65   $155.70  
  Purchase #7 $204.80   5.130%   $215.3062   $215.31   $215.30   $215.30  
  7 purchase totals = $1,014.61       $1,112.2025   $1,112.21   $1,112.15   $1,112.30