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 $166.53   11.700%   $186.014   $186.01   $186.00   $186.00  
  Purchase #2 $206.29   7.596%   $221.9598   $221.96   $221.95   $222.00  
  Purchase #3 $139.52   9.581%   $152.8874   $152.89   $152.90   $152.90  
  Purchase #4 $55.96   10.271%   $61.7077   $61.71   $61.70   $61.70  
  Purchase #5 $146.55   11.306%   $163.1189   $163.12   $163.10   $163.10  
  Purchase #6 $236.95   6.760%   $252.9678   $252.97   $252.95   $253.00  
  Purchase #7 $43.37   6.692%   $46.2723   $46.27   $46.25   $46.30  
  7 purchase totals = $995.17       $1,084.9279   $1,084.93   $1,084.85   $1,085.00