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 $54.41   6.558%   $57.9782   $57.98   $58.00   $58.00  
  Purchase #2 $58.63   4.146%   $61.0608   $61.06   $61.05   $61.10  
  Purchase #3 $229.68   7.144%   $246.0883   $246.09   $246.10   $246.10  
  Purchase #4 $215.94   5.381%   $227.5597   $227.56   $227.55   $227.60  
  Purchase #5 $167.45   7.577%   $180.1377   $180.14   $180.15   $180.10  
  Purchase #6 $227.42   7.530%   $244.5447   $244.54   $244.55   $244.50  
  Purchase #7 $27.56   12.410%   $30.9802   $30.98   $31.00   $31.00  
  7 purchase totals = $981.09       $1,048.3496   $1,048.35   $1,048.40   $1,048.40