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 $234.67   3.452%   $242.7708   $242.77   $242.75   $242.80  
  Purchase #2 $65.33   4.715%   $68.4103   $68.41   $68.40   $68.40  
  Purchase #3 $106.58   13.429%   $120.8926   $120.89   $120.90   $120.90  
  Purchase #4 $112.45   13.335%   $127.4452   $127.45   $127.45   $127.40  
  Purchase #5 $143.25   5.867%   $151.6545   $151.65   $151.65   $151.70  
  Purchase #6 $96.65   9.781%   $106.1033   $106.10   $106.10   $106.10  
  Purchase #7 $202.67   8.419%   $219.7328   $219.73   $219.75   $219.70  
  7 purchase totals = $961.60       $1,037.0095   $1,037.00   $1,037.00   $1,037.00