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 $206.56   13.777%   $235.0178   $235.02   $235.00   $235.00  
  Purchase #2 $192.74   7.551%   $207.2938   $207.29   $207.30   $207.30  
  Purchase #3 $31.45   11.851%   $35.1771   $35.18   $35.20   $35.20  
  Purchase #4 $135.46   3.612%   $140.3528   $140.35   $140.35   $140.40  
  Purchase #5 $154.95   6.415%   $164.89   $164.89   $164.90   $164.90  
  Purchase #6 $193.81   11.363%   $215.8326   $215.83   $215.85   $215.80  
  Purchase #7 $31.68   7.135%   $33.9404   $33.94   $33.95   $33.90  
  7 purchase totals = $946.65       $1,032.5045   $1,032.50   $1,032.55   $1,032.50