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 $64.29   8.448%   $69.7212   $69.72   $69.70   $69.70  
  Purchase #2 $137.91   8.420%   $149.522   $149.52   $149.50   $149.50  
  Purchase #3 $92.49   3.455%   $95.6855   $95.69   $95.70   $95.70  
  Purchase #4 $202.96   4.695%   $212.489   $212.49   $212.50   $212.50  
  Purchase #5 $24.97   8.375%   $27.0612   $27.06   $27.05   $27.10  
  Purchase #6 $250.52   6.451%   $266.681   $266.68   $266.70   $266.70  
  Purchase #7 $183.89   7.415%   $197.5254   $197.53   $197.55   $197.50  
  7 purchase totals = $957.03       $1,018.6853   $1,018.69   $1,018.70   $1,018.70