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 $61.29   8.229%   $66.3336   $66.33   $66.35   $66.30  
  Purchase #2 $206.71   10.640%   $228.7039   $228.70   $228.70   $228.70  
  Purchase #3 $189.72   3.545%   $196.4456   $196.45   $196.45   $196.40  
  Purchase #4 $225.60   7.207%   $241.859   $241.86   $241.85   $241.90  
  Purchase #5 $214.54   3.253%   $221.519   $221.52   $221.50   $221.50  
  Purchase #6 $102.44   10.459%   $113.1542   $113.15   $113.15   $113.20  
  Purchase #7 $118.35   6.176%   $125.6593   $125.66   $125.65   $125.70  
  7 purchase totals = $1,118.65       $1,193.6746   $1,193.67   $1,193.65   $1,193.70