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 $55.42   11.499%   $61.7927   $61.79   $61.80   $61.80  
  Purchase #2 $79.96   8.378%   $86.659   $86.66   $86.65   $86.70  
  Purchase #3 $31.34   11.654%   $34.9924   $34.99   $35.00   $35.00  
  Purchase #4 $74.28   12.258%   $83.3852   $83.39   $83.40   $83.40  
  Purchase #5 $230.29   5.642%   $243.283   $243.28   $243.30   $243.30  
  Purchase #6 $132.66   11.248%   $147.5816   $147.58   $147.60   $147.60  
  Purchase #7 $117.69   12.628%   $132.5519   $132.55   $132.55   $132.60  
  7 purchase totals = $721.64       $790.2458   $790.24   $790.30   $790.40