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 $203.52   11.803%   $227.5415   $227.54   $227.55   $227.50  
  Purchase #2 $213.94   4.393%   $223.3384   $223.34   $223.35   $223.30  
  Purchase #3 $32.46   5.782%   $34.3368   $34.34   $34.35   $34.30  
  Purchase #4 $225.44   3.294%   $232.866   $232.87   $232.85   $232.90  
  Purchase #5 $96.69   13.782%   $110.0158   $110.02   $110.00   $110.00  
  Purchase #6 $141.77   12.260%   $159.151   $159.15   $159.15   $159.20  
  Purchase #7 $219.78   4.172%   $228.9492   $228.95   $228.95   $228.90  
  7 purchase totals = $1,133.60       $1,216.1987   $1,216.21   $1,216.20   $1,216.10