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 $58.47   11.196%   $65.0163   $65.02   $65.00   $65.00  
  Purchase #2 $215.35   4.433%   $224.8965   $224.90   $224.90   $224.90  
  Purchase #3 $50.62   12.558%   $56.9769   $56.98   $57.00   $57.00  
  Purchase #4 $190.95   11.109%   $212.1626   $212.16   $212.15   $212.20  
  Purchase #5 $175.33   4.646%   $183.4758   $183.48   $183.50   $183.50  
  Purchase #6 $210.33   10.259%   $231.9078   $231.91   $231.90   $231.90  
  Purchase #7 $193.34   5.430%   $203.8384   $203.84   $203.85   $203.80  
  7 purchase totals = $1,094.39       $1,178.2743   $1,178.29   $1,178.30   $1,178.30