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 $145.68   5.186%   $153.235   $153.24   $153.25   $153.20  
  Purchase #2 $10.89   3.554%   $11.277   $11.28   $11.30   $11.30  
  Purchase #3 $67.36   8.488%   $73.0775   $73.08   $73.10   $73.10  
  Purchase #4 $106.87   12.459%   $120.1849   $120.18   $120.20   $120.20  
  Purchase #5 $190.70   6.464%   $203.0268   $203.03   $203.05   $203.00  
  Purchase #6 $176.54   9.863%   $193.9521   $193.95   $193.95   $194.00  
  Purchase #7 $8.84   5.645%   $9.339   $9.34   $9.35   $9.30  
  7 purchase totals = $706.88       $764.0923   $764.10   $764.20   $764.10