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 $153.28   6.683%   $163.5237   $163.52   $163.50   $163.50  
  Purchase #2 $88.36   5.872%   $93.5485   $93.55   $93.55   $93.50  
  Purchase #3 $15.79   10.589%   $17.462   $17.46   $17.45   $17.50  
  Purchase #4 $245.60   12.836%   $277.1252   $277.13   $277.15   $277.10  
  Purchase #5 $197.65   7.612%   $212.6951   $212.70   $212.70   $212.70  
  Purchase #6 $152.70   8.397%   $165.5222   $165.52   $165.50   $165.50  
  Purchase #7 $39.98   4.147%   $41.638   $41.64   $41.65   $41.60  
  7 purchase totals = $893.36       $971.5147   $971.52   $971.50   $971.40