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 $202.81   11.456%   $226.0439   $226.04   $226.05   $226.00  
  Purchase #2 $61.61   3.244%   $63.6086   $63.61   $63.60   $63.60  
  Purchase #3 $147.49   13.181%   $166.9307   $166.93   $166.95   $166.90  
  Purchase #4 $207.30   5.802%   $219.3275   $219.33   $219.35   $219.30  
  Purchase #5 $203.90   9.305%   $222.8729   $222.87   $222.85   $222.90  
  Purchase #6 $96.90   13.757%   $110.2305   $110.23   $110.25   $110.20  
  Purchase #7 $27.73   4.756%   $29.0488   $29.05   $29.05   $29.00  
  7 purchase totals = $947.74       $1,038.0629   $1,038.06   $1,038.10   $1,037.90