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 $142.98   5.587%   $150.9683   $150.97   $150.95   $151.00  
  Purchase #2 $166.38   12.352%   $186.9313   $186.93   $186.95   $186.90  
  Purchase #3 $41.79   5.414%   $44.0525   $44.05   $44.05   $44.10  
  Purchase #4 $234.74   5.511%   $247.6765   $247.68   $247.70   $247.70  
  Purchase #5 $210.63   12.612%   $237.1947   $237.19   $237.20   $237.20  
  Purchase #6 $184.99   3.362%   $191.2094   $191.21   $191.20   $191.20  
  Purchase #7 $144.46   13.181%   $163.5013   $163.50   $163.50   $163.50  
  7 purchase totals = $1,125.97       $1,221.5340   $1,221.53   $1,221.55   $1,221.60