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 $211.47   12.126%   $237.1129   $237.11   $237.10   $237.10  
  Purchase #2 $21.59   9.196%   $23.5754   $23.58   $23.60   $23.60  
  Purchase #3 $122.57   4.199%   $127.7167   $127.72   $127.70   $127.70  
  Purchase #4 $215.55   4.765%   $225.821   $225.82   $225.80   $225.80  
  Purchase #5 $209.34   13.720%   $238.0614   $238.06   $238.05   $238.10  
  Purchase #6 $97.67   9.195%   $106.6508   $106.65   $106.65   $106.70  
  Purchase #7 $49.45   7.709%   $53.2621   $53.26   $53.25   $53.30  
  7 purchase totals = $927.64       $1,012.2003   $1,012.20   $1,012.15   $1,012.30