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 $53.63   8.263%   $58.0614   $58.06   $58.05   $58.10  
  Purchase #2 $239.37   13.633%   $272.0033   $272.00   $272.00   $272.00  
  Purchase #3 $191.62   5.827%   $202.7857   $202.79   $202.80   $202.80  
  Purchase #4 $244.91   9.829%   $268.9822   $268.98   $269.00   $269.00  
  Purchase #5 $51.46   6.605%   $54.8589   $54.86   $54.85   $54.90  
  Purchase #6 $134.60   13.107%   $152.242   $152.24   $152.25   $152.20  
  Purchase #7 $56.47   8.488%   $61.2632   $61.26   $61.25   $61.30  
  7 purchase totals = $972.06       $1,070.1967   $1,070.19   $1,070.20   $1,070.30