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 $66.66   10.297%   $73.524   $73.52   $73.50   $73.50  
  Purchase #2 $226.68   8.813%   $246.6573   $246.66   $246.65   $246.70  
  Purchase #3 $79.69   5.247%   $83.8713   $83.87   $83.85   $83.90  
  Purchase #4 $248.30   7.840%   $267.7667   $267.77   $267.75   $267.80  
  Purchase #5 $67.28   3.214%   $69.4424   $69.44   $69.45   $69.40  
  Purchase #6 $191.57   11.636%   $213.8611   $213.86   $213.85   $213.90  
  Purchase #7 $161.73   11.740%   $180.7171   $180.72   $180.70   $180.70  
  7 purchase totals = $1,041.91       $1,135.8399   $1,135.84   $1,135.75   $1,135.90