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 $94.43   3.420%   $97.6595   $97.66   $97.65   $97.70  
  Purchase #2 $79.51   7.148%   $85.1934   $85.19   $85.20   $85.20  
  Purchase #3 $41.66   7.335%   $44.7158   $44.72   $44.70   $44.70  
  Purchase #4 $207.46   8.774%   $225.6625   $225.66   $225.65   $225.70  
  Purchase #5 $27.72   12.466%   $31.1756   $31.18   $31.20   $31.20  
  Purchase #6 $240.46   12.175%   $269.736   $269.74   $269.75   $269.70  
  Purchase #7 $220.61   12.770%   $248.7819   $248.78   $248.80   $248.80  
  7 purchase totals = $911.85       $1,002.9247   $1,002.93   $1,002.95   $1,003.00