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 $52.79   8.562%   $57.3099   $57.31   $57.30   $57.30  
  Purchase #2 $215.52   10.131%   $237.3543   $237.35   $237.35   $237.40  
  Purchase #3 $204.26   10.556%   $225.8217   $225.82   $225.80   $225.80  
  Purchase #4 $150.36   8.449%   $163.0639   $163.06   $163.05   $163.10  
  Purchase #5 $131.94   13.683%   $149.9934   $149.99   $150.00   $150.00  
  Purchase #6 $170.43   8.602%   $185.0904   $185.09   $185.10   $185.10  
  Purchase #7 $160.39   10.476%   $177.1925   $177.19   $177.20   $177.20  
  7 purchase totals = $1,085.69       $1,195.8261   $1,195.81   $1,195.80   $1,195.90