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 $204.82   13.746%   $232.9746   $232.97   $232.95   $233.00  
  Purchase #2 $186.65   9.718%   $204.7886   $204.79   $204.80   $204.80  
  Purchase #3 $141.70   3.229%   $146.2755   $146.28   $146.30   $146.30  
  Purchase #4 $214.87   3.585%   $222.5731   $222.57   $222.55   $222.60  
  Purchase #5 $30.93   3.782%   $32.0998   $32.10   $32.10   $32.10  
  Purchase #6 $179.96   6.633%   $191.8967   $191.90   $191.90   $191.90  
  Purchase #7 $216.52   9.481%   $237.0483   $237.05   $237.05   $237.00  
  7 purchase totals = $1,175.45       $1,267.6566   $1,267.66   $1,267.65   $1,267.70