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 $25.33   8.849%   $27.5715   $27.57   $27.55   $27.60  
  Purchase #2 $243.37   13.829%   $277.0256   $277.03   $277.05   $277.00  
  Purchase #3 $46.69   12.652%   $52.5972   $52.60   $52.60   $52.60  
  Purchase #4 $213.92   9.496%   $234.2338   $234.23   $234.25   $234.20  
  Purchase #5 $186.60   9.761%   $204.814   $204.81   $204.80   $204.80  
  Purchase #6 $222.98   4.125%   $232.1779   $232.18   $232.20   $232.20  
  Purchase #7 $22.86   9.517%   $25.0356   $25.04   $25.05   $25.00  
  7 purchase totals = $961.75       $1,053.4556   $1,053.46   $1,053.50   $1,053.40