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 $202.37   4.712%   $211.9057   $211.91   $211.90   $211.90  
  Purchase #2 $50.92   13.825%   $57.9597   $57.96   $57.95   $58.00  
  Purchase #3 $18.92   3.797%   $19.6384   $19.64   $19.65   $19.60  
  Purchase #4 $83.63   12.303%   $93.919   $93.92   $93.90   $93.90  
  Purchase #5 $229.44   5.679%   $242.4699   $242.47   $242.45   $242.50  
  Purchase #6 $150.60   12.561%   $169.5169   $169.52   $169.50   $169.50  
  Purchase #7 $190.49   11.619%   $212.623   $212.62   $212.60   $212.60  
  7 purchase totals = $926.37       $1,008.0326   $1,008.04   $1,007.95   $1,008.00