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 $162.70   10.622%   $179.982   $179.98   $180.00   $180.00  
  Purchase #2 $203.90   10.357%   $225.0179   $225.02   $225.00   $225.00  
  Purchase #3 $60.64   6.297%   $64.4585   $64.46   $64.45   $64.50  
  Purchase #4 $31.94   8.462%   $34.6428   $34.64   $34.65   $34.60  
  Purchase #5 $147.78   10.551%   $163.3723   $163.37   $163.35   $163.40  
  Purchase #6 $214.74   13.314%   $243.3305   $243.33   $243.35   $243.30  
  Purchase #7 $48.85   11.276%   $54.3583   $54.36   $54.35   $54.40  
  7 purchase totals = $870.55       $965.1623   $965.16   $965.15   $965.20