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 $181.76   12.243%   $204.0129   $204.01   $204.00   $204.00  
  Purchase #2 $151.40   3.770%   $157.1078   $157.11   $157.10   $157.10  
  Purchase #3 $233.73   3.866%   $242.766   $242.77   $242.75   $242.80  
  Purchase #4 $26.40   12.515%   $29.704   $29.70   $29.70   $29.70  
  Purchase #5 $147.76   5.629%   $156.0774   $156.08   $156.10   $156.10  
  Purchase #6 $165.75   12.665%   $186.7422   $186.74   $186.75   $186.70  
  Purchase #7 $27.75   12.109%   $31.1102   $31.11   $31.10   $31.10  
  7 purchase totals = $934.55       $1,007.5205   $1,007.52   $1,007.50   $1,007.50