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 $201.75   11.638%   $225.2297   $225.23   $225.25   $225.20  
  Purchase #2 $166.35   3.160%   $171.6067   $171.61   $171.60   $171.60  
  Purchase #3 $50.90   6.273%   $54.093   $54.09   $54.10   $54.10  
  Purchase #4 $233.84   13.250%   $264.8238   $264.82   $264.80   $264.80  
  Purchase #5 $5.81   7.591%   $6.251   $6.25   $6.25   $6.30  
  Purchase #6 $192.30   3.488%   $199.0074   $199.01   $199.00   $199.00  
  Purchase #7 $74.45   13.736%   $84.6765   $84.68   $84.70   $84.70  
  7 purchase totals = $925.40       $1,005.6881   $1,005.69   $1,005.70   $1,005.70