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 $202.44   10.586%   $223.8703   $223.87   $223.85   $223.90  
  Purchase #2 $210.76   4.147%   $219.5002   $219.50   $219.50   $219.50  
  Purchase #3 $44.72   6.693%   $47.7131   $47.71   $47.70   $47.70  
  Purchase #4 $206.55   13.796%   $235.0456   $235.05   $235.05   $235.00  
  Purchase #5 $124.66   13.389%   $141.3507   $141.35   $141.35   $141.40  
  Purchase #6 $10.45   6.341%   $11.1126   $11.11   $11.10   $11.10  
  Purchase #7 $147.64   4.238%   $153.897   $153.90   $153.90   $153.90  
  7 purchase totals = $947.22       $1,032.4895   $1,032.49   $1,032.45   $1,032.50