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 $181.86   12.154%   $203.9633   $203.96   $203.95   $204.00  
  Purchase #2 $228.62   13.775%   $260.1124   $260.11   $260.10   $260.10  
  Purchase #3 $65.35   13.611%   $74.2448   $74.24   $74.25   $74.20  
  Purchase #4 $156.98   13.702%   $178.4894   $178.49   $178.50   $178.50  
  Purchase #5 $165.77   12.143%   $185.8995   $185.90   $185.90   $185.90  
  Purchase #6 $24.91   4.864%   $26.1216   $26.12   $26.10   $26.10  
  Purchase #7 $97.75   4.264%   $101.9181   $101.92   $101.90   $101.90  
  7 purchase totals = $921.24       $1,030.7491   $1,030.74   $1,030.70   $1,030.70