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 $64.53   8.370%   $69.9312   $69.93   $69.95   $69.90  
  Purchase #2 $221.28   8.577%   $240.2592   $240.26   $240.25   $240.30  
  Purchase #3 $160.40   3.191%   $165.5184   $165.52   $165.50   $165.50  
  Purchase #4 $171.32   11.765%   $191.4758   $191.48   $191.50   $191.50  
  Purchase #5 $237.71   3.757%   $246.6408   $246.64   $246.65   $246.60  
  Purchase #6 $113.46   12.794%   $127.9761   $127.98   $128.00   $128.00  
  Purchase #7 $165.55   3.532%   $171.3972   $171.40   $171.40   $171.40  
  7 purchase totals = $1,134.25       $1,213.1987   $1,213.21   $1,213.25   $1,213.20