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 $198.61   10.113%   $218.6954   $218.70   $218.70   $218.70  
  Purchase #2 $126.31   13.780%   $143.7155   $143.72   $143.70   $143.70  
  Purchase #3 $45.59   9.277%   $49.8194   $49.82   $49.80   $49.80  
  Purchase #4 $214.74   13.381%   $243.4744   $243.47   $243.45   $243.50  
  Purchase #5 $19.46   13.102%   $22.0096   $22.01   $22.00   $22.00  
  Purchase #6 $168.29   11.257%   $187.2344   $187.23   $187.25   $187.20  
  Purchase #7 $202.73   8.472%   $219.9053   $219.91   $219.90   $219.90  
  7 purchase totals = $975.73       $1,084.8540   $1,084.86   $1,084.80   $1,084.80