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 $43.40   3.756%   $45.0301   $45.03   $45.05   $45.00  
  Purchase #2 $212.31   3.397%   $219.5222   $219.52   $219.50   $219.50  
  Purchase #3 $203.81   5.112%   $214.2288   $214.23   $214.25   $214.20  
  Purchase #4 $244.55   8.806%   $266.0851   $266.09   $266.10   $266.10  
  Purchase #5 $72.78   7.162%   $77.9925   $77.99   $78.00   $78.00  
  Purchase #6 $79.74   3.170%   $82.2678   $82.27   $82.25   $82.30  
  Purchase #7 $137.78   8.325%   $149.2502   $149.25   $149.25   $149.30  
  7 purchase totals = $994.37       $1,054.3767   $1,054.38   $1,054.40   $1,054.40