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 $20.51   13.561%   $23.2914   $23.29   $23.30   $23.30  
  Purchase #2 $184.58   4.846%   $193.5247   $193.52   $193.50   $193.50  
  Purchase #3 $222.71   4.172%   $232.0015   $232.00   $232.00   $232.00  
  Purchase #4 $55.80   8.440%   $60.5095   $60.51   $60.50   $60.50  
  Purchase #5 $112.76   7.572%   $121.2982   $121.30   $121.30   $121.30  
  Purchase #6 $181.55   6.494%   $193.3399   $193.34   $193.35   $193.30  
  Purchase #7 $176.97   6.106%   $187.7758   $187.78   $187.80   $187.80  
  7 purchase totals = $954.88       $1,011.7410   $1,011.74   $1,011.75   $1,011.70