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 $153.93   7.639%   $165.6887   $165.69   $165.70   $165.70  
  Purchase #2 $96.93   6.234%   $102.9726   $102.97   $102.95   $103.00  
  Purchase #3 $67.43   8.440%   $73.1211   $73.12   $73.10   $73.10  
  Purchase #4 $167.33   12.837%   $188.8102   $188.81   $188.80   $188.80  
  Purchase #5 $139.25   8.405%   $150.954   $150.95   $150.95   $151.00  
  Purchase #6 $188.90   7.433%   $202.9409   $202.94   $202.95   $202.90  
  Purchase #7 $180.72   3.324%   $186.7271   $186.73   $186.75   $186.70  
  7 purchase totals = $994.49       $1,071.2146   $1,071.21   $1,071.20   $1,071.20