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 $131.98   13.551%   $149.8646   $149.86   $149.85   $149.90  
  Purchase #2 $192.65   10.214%   $212.3273   $212.33   $212.35   $212.30  
  Purchase #3 $131.74   12.473%   $148.1719   $148.17   $148.15   $148.20  
  Purchase #4 $56.74   8.561%   $61.5975   $61.60   $61.60   $61.60  
  Purchase #5 $87.67   13.151%   $99.1995   $99.20   $99.20   $99.20  
  Purchase #6 $118.66   7.866%   $127.9938   $127.99   $128.00   $128.00  
  Purchase #7 $201.35   7.575%   $216.6023   $216.60   $216.60   $216.60  
  7 purchase totals = $920.79       $1,015.7569   $1,015.75   $1,015.75   $1,015.80