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 $62.51   9.173%   $68.244   $68.24   $68.25   $68.20  
  Purchase #2 $204.51   12.188%   $229.4357   $229.44   $229.45   $229.40  
  Purchase #3 $51.80   9.238%   $56.5853   $56.59   $56.60   $56.60  
  Purchase #4 $201.69   6.496%   $214.7918   $214.79   $214.80   $214.80  
  Purchase #5 $165.60   6.582%   $176.4998   $176.50   $176.50   $176.50  
  Purchase #6 $58.52   7.360%   $62.8271   $62.83   $62.85   $62.80  
  Purchase #7 $190.46   11.367%   $212.1096   $212.11   $212.10   $212.10  
  7 purchase totals = $935.09       $1,020.4933   $1,020.50   $1,020.55   $1,020.40