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 $216.96   3.382%   $224.2976   $224.30   $224.30   $224.30  
  Purchase #2 $124.26   11.837%   $138.9687   $138.97   $138.95   $139.00  
  Purchase #3 $37.92   9.818%   $41.643   $41.64   $41.65   $41.60  
  Purchase #4 $193.62   11.443%   $215.7759   $215.78   $215.80   $215.80  
  Purchase #5 $99.37   3.808%   $103.154   $103.15   $103.15   $103.20  
  Purchase #6 $55.48   9.289%   $60.6335   $60.63   $60.65   $60.60  
  Purchase #7 $200.95   13.592%   $228.2631   $228.26   $228.25   $228.30  
  7 purchase totals = $928.56       $1,012.7358   $1,012.73   $1,012.75   $1,012.80