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 $171.28   8.462%   $185.7737   $185.77   $185.75   $185.80  
  Purchase #2 $164.51   9.145%   $179.5544   $179.55   $179.55   $179.60  
  Purchase #3 $171.78   7.235%   $184.2083   $184.21   $184.20   $184.20  
  Purchase #4 $246.62   5.407%   $259.9547   $259.95   $259.95   $260.00  
  Purchase #5 $186.96   8.858%   $203.5209   $203.52   $203.50   $203.50  
  Purchase #6 $150.91   6.225%   $160.3041   $160.30   $160.30   $160.30  
  Purchase #7 $31.55   8.331%   $34.1784   $34.18   $34.20   $34.20  
  7 purchase totals = $1,123.61       $1,207.4945   $1,207.48   $1,207.45   $1,207.60