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 $249.94   13.218%   $282.9771   $282.98   $283.00   $283.00  
  Purchase #2 $29.76   12.344%   $33.4336   $33.43   $33.45   $33.40  
  Purchase #3 $243.62   11.699%   $272.1211   $272.12   $272.10   $272.10  
  Purchase #4 $183.33   13.234%   $207.5919   $207.59   $207.60   $207.60  
  Purchase #5 $208.87   7.868%   $225.3039   $225.30   $225.30   $225.30  
  Purchase #6 $239.84   8.278%   $259.694   $259.69   $259.70   $259.70  
  Purchase #7 $172.39   11.384%   $192.0149   $192.01   $192.00   $192.00  
  7 purchase totals = $1,327.75       $1,473.1365   $1,473.12   $1,473.15   $1,473.10