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 $59.27   9.705%   $65.0222   $65.02   $65.00   $65.00  
  Purchase #2 $82.91   13.331%   $93.9627   $93.96   $93.95   $94.00  
  Purchase #3 $191.67   8.741%   $208.4239   $208.42   $208.40   $208.40  
  Purchase #4 $148.42   11.310%   $165.2063   $165.21   $165.20   $165.20  
  Purchase #5 $229.92   5.806%   $243.2692   $243.27   $243.25   $243.30  
  Purchase #6 $219.52   11.210%   $244.1282   $244.13   $244.15   $244.10  
  Purchase #7 $157.99   13.633%   $179.5288   $179.53   $179.55   $179.50  
  7 purchase totals = $1,089.70       $1,199.5413   $1,199.54   $1,199.50   $1,199.50