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 $141.37   3.463%   $146.2656   $146.27   $146.25   $146.30  
  Purchase #2 $63.97   11.182%   $71.1231   $71.12   $71.10   $71.10  
  Purchase #3 $131.52   10.774%   $145.69   $145.69   $145.70   $145.70  
  Purchase #4 $113.34   8.187%   $122.6191   $122.62   $122.60   $122.60  
  Purchase #5 $22.92   5.179%   $24.107   $24.11   $24.10   $24.10  
  Purchase #6 $165.61   5.662%   $174.9868   $174.99   $175.00   $175.00  
  Purchase #7 $59.88   9.490%   $65.5626   $65.56   $65.55   $65.60  
  7 purchase totals = $698.61       $750.3542   $750.36   $750.30   $750.40