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 $29.68   11.482%   $33.0879   $33.09   $33.10   $33.10  
  Purchase #2 $232.52   12.212%   $260.9153   $260.92   $260.90   $260.90  
  Purchase #3 $98.75   8.106%   $106.7547   $106.75   $106.75   $106.80  
  Purchase #4 $221.28   4.289%   $230.7707   $230.77   $230.75   $230.80  
  Purchase #5 $227.53   3.609%   $235.7416   $235.74   $235.75   $235.70  
  Purchase #6 $147.87   11.336%   $164.6325   $164.63   $164.65   $164.60  
  Purchase #7 $85.33   10.461%   $94.2564   $94.26   $94.25   $94.30  
  7 purchase totals = $1,042.96       $1,126.1591   $1,126.16   $1,126.15   $1,126.20