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 $59.44   8.772%   $64.6541   $64.65   $64.65   $64.70  
  Purchase #2 $202.97   7.404%   $217.9979   $218.00   $218.00   $218.00  
  Purchase #3 $77.59   9.656%   $85.0821   $85.08   $85.10   $85.10  
  Purchase #4 $110.92   9.369%   $121.3121   $121.31   $121.30   $121.30  
  Purchase #5 $72.49   8.311%   $78.5146   $78.51   $78.50   $78.50  
  Purchase #6 $219.25   12.179%   $245.9525   $245.95   $245.95   $246.00  
  Purchase #7 $113.40   8.630%   $123.1864   $123.19   $123.20   $123.20  
  7 purchase totals = $856.06       $936.6997   $936.69   $936.70   $936.80