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 $211.86   12.262%   $237.8383   $237.84   $237.85   $237.80  
  Purchase #2 $53.91   13.663%   $61.2757   $61.28   $61.30   $61.30  
  Purchase #3 $187.37   8.301%   $202.9236   $202.92   $202.90   $202.90  
  Purchase #4 $250.58   9.770%   $275.0617   $275.06   $275.05   $275.10  
  Purchase #5 $72.56   13.750%   $82.537   $82.54   $82.55   $82.50  
  Purchase #6 $23.34   3.753%   $24.216   $24.22   $24.20   $24.20  
  Purchase #7 $206.40   8.376%   $223.6881   $223.69   $223.70   $223.70  
  7 purchase totals = $1,006.02       $1,107.5404   $1,107.55   $1,107.55   $1,107.50