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 $104.46   6.577%   $111.3303   $111.33   $111.35   $111.30  
  Purchase #2 $176.85   10.371%   $195.1911   $195.19   $195.20   $195.20  
  Purchase #3 $31.74   4.850%   $33.2794   $33.28   $33.30   $33.30  
  Purchase #4 $41.92   3.416%   $43.352   $43.35   $43.35   $43.40  
  Purchase #5 $176.55   8.847%   $192.1694   $192.17   $192.15   $192.20  
  Purchase #6 $233.26   13.533%   $264.8271   $264.83   $264.85   $264.80  
  Purchase #7 $178.51   13.470%   $202.5553   $202.56   $202.55   $202.60  
  7 purchase totals = $943.29       $1,042.7046   $1,042.71   $1,042.75   $1,042.80