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 $88.51   6.788%   $94.5181   $94.52   $94.50   $94.50  
  Purchase #2 $219.65   12.140%   $246.3155   $246.32   $246.30   $246.30  
  Purchase #3 $171.64   3.183%   $177.1033   $177.10   $177.10   $177.10  
  Purchase #4 $27.55   9.704%   $30.2235   $30.22   $30.20   $30.20  
  Purchase #5 $215.33   7.771%   $232.0633   $232.06   $232.05   $232.10  
  Purchase #6 $51.85   12.317%   $58.2364   $58.24   $58.25   $58.20  
  Purchase #7 $204.49   8.641%   $222.16   $222.16   $222.15   $222.20  
  7 purchase totals = $979.02       $1,060.6201   $1,060.62   $1,060.55   $1,060.60