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 $243.37   11.853%   $272.2166   $272.22   $272.20   $272.20  
  Purchase #2 $211.70   6.121%   $224.6582   $224.66   $224.65   $224.70  
  Purchase #3 $30.70   6.349%   $32.6491   $32.65   $32.65   $32.60  
  Purchase #4 $85.62   11.345%   $95.3336   $95.33   $95.35   $95.30  
  Purchase #5 $93.65   3.241%   $96.6852   $96.69   $96.70   $96.70  
  Purchase #6 $119.32   3.659%   $123.6859   $123.69   $123.70   $123.70  
  Purchase #7 $153.35   8.746%   $166.762   $166.76   $166.75   $166.80  
  7 purchase totals = $937.71       $1,011.9906   $1,012.00   $1,012.00   $1,012.00