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 $33.30   12.662%   $37.5164   $37.52   $37.50   $37.50  
  Purchase #2 $192.62   7.433%   $206.9374   $206.94   $206.95   $206.90  
  Purchase #3 $16.76   8.364%   $18.1618   $18.16   $18.15   $18.20  
  Purchase #4 $220.39   12.539%   $248.0247   $248.02   $248.00   $248.00  
  Purchase #5 $120.78   7.672%   $130.0462   $130.05   $130.05   $130.00  
  Purchase #6 $222.55   10.824%   $246.6388   $246.64   $246.65   $246.60  
  Purchase #7 $148.71   8.263%   $160.9979   $161.00   $161.00   $161.00  
  7 purchase totals = $955.11       $1,048.3232   $1,048.33   $1,048.30   $1,048.20