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 $82.76   10.319%   $91.3   $91.30   $91.30   $91.30  
  Purchase #2 $23.65   11.815%   $26.4442   $26.44   $26.45   $26.40  
  Purchase #3 $180.89   4.850%   $189.6632   $189.66   $189.65   $189.70  
  Purchase #4 $243.62   13.574%   $276.689   $276.69   $276.70   $276.70  
  Purchase #5 $33.99   7.383%   $36.4995   $36.50   $36.50   $36.50  
  Purchase #6 $215.79   12.820%   $243.4543   $243.45   $243.45   $243.50  
  Purchase #7 $176.45   11.169%   $196.1577   $196.16   $196.15   $196.20  
  7 purchase totals = $957.15       $1,060.2079   $1,060.20   $1,060.20   $1,060.30