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 $218.52   10.379%   $241.2002   $241.20   $241.20   $241.20  
  Purchase #2 $97.45   6.820%   $104.0961   $104.10   $104.10   $104.10  
  Purchase #3 $181.98   4.800%   $190.715   $190.72   $190.70   $190.70  
  Purchase #4 $45.96   4.106%   $47.8471   $47.85   $47.85   $47.80  
  Purchase #5 $190.41   9.731%   $208.9388   $208.94   $208.95   $208.90  
  Purchase #6 $90.60   3.793%   $94.0365   $94.04   $94.05   $94.00  
  Purchase #7 $212.99   6.111%   $226.0058   $226.01   $226.00   $226.00  
  7 purchase totals = $1,037.91       $1,112.8395   $1,112.86   $1,112.85   $1,112.70