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 $164.41   5.419%   $173.3194   $173.32   $173.30   $173.30  
  Purchase #2 $220.26   11.169%   $244.8608   $244.86   $244.85   $244.90  
  Purchase #3 $160.96   6.171%   $170.8928   $170.89   $170.90   $170.90  
  Purchase #4 $246.80   8.188%   $267.008   $267.01   $267.00   $267.00  
  Purchase #5 $81.50   6.865%   $87.095   $87.10   $87.10   $87.10  
  Purchase #6 $46.28   4.729%   $48.4686   $48.47   $48.45   $48.50  
  Purchase #7 $209.55   10.798%   $232.1772   $232.18   $232.20   $232.20  
  7 purchase totals = $1,129.76       $1,223.8218   $1,223.83   $1,223.80   $1,223.90