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 $176.52   9.456%   $193.2117   $193.21   $193.20   $193.20  
  Purchase #2 $96.98   7.537%   $104.2894   $104.29   $104.30   $104.30  
  Purchase #3 $118.43   5.567%   $125.023   $125.02   $125.00   $125.00  
  Purchase #4 $83.86   5.694%   $88.635   $88.64   $88.65   $88.60  
  Purchase #5 $220.66   13.552%   $250.5638   $250.56   $250.55   $250.60  
  Purchase #6 $241.83   3.604%   $250.5456   $250.55   $250.55   $250.50  
  Purchase #7 $207.78   7.662%   $223.7001   $223.70   $223.70   $223.70  
  7 purchase totals = $1,146.06       $1,235.9686   $1,235.97   $1,235.95   $1,235.90