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 $132.92   13.832%   $151.3055   $151.31   $151.30   $151.30  
  Purchase #2 $186.98   8.201%   $202.3142   $202.31   $202.30   $202.30  
  Purchase #3 $162.55   5.841%   $172.0445   $172.04   $172.05   $172.00  
  Purchase #4 $206.45   4.664%   $216.0788   $216.08   $216.10   $216.10  
  Purchase #5 $161.54   5.325%   $170.142   $170.14   $170.15   $170.10  
  Purchase #6 $153.94   13.319%   $174.4433   $174.44   $174.45   $174.40  
  Purchase #7 $246.28   10.281%   $271.6   $271.60   $271.60   $271.60  
  7 purchase totals = $1,250.66       $1,357.9283   $1,357.92   $1,357.95   $1,357.80