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 $61.39   11.216%   $68.2755   $68.28   $68.30   $68.30  
  Purchase #2 $240.97   8.295%   $260.9585   $260.96   $260.95   $261.00  
  Purchase #3 $174.36   3.294%   $180.1034   $180.10   $180.10   $180.10  
  Purchase #4 $118.88   3.445%   $122.9754   $122.98   $123.00   $123.00  
  Purchase #5 $170.76   3.802%   $177.2523   $177.25   $177.25   $177.30  
  Purchase #6 $191.70   4.138%   $199.6325   $199.63   $199.65   $199.60  
  Purchase #7 $203.80   4.187%   $212.3331   $212.33   $212.35   $212.30  
  7 purchase totals = $1,161.86       $1,221.5307   $1,221.53   $1,221.60   $1,221.60