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 $54.37   8.267%   $58.8648   $58.86   $58.85   $58.90  
  Purchase #2 $236.99   12.829%   $267.3934   $267.39   $267.40   $267.40  
  Purchase #3 $160.99   7.470%   $173.016   $173.02   $173.00   $173.00  
  Purchase #4 $200.52   8.731%   $218.0274   $218.03   $218.05   $218.00  
  Purchase #5 $109.65   13.568%   $124.5273   $124.53   $124.55   $124.50  
  Purchase #6 $123.37   8.317%   $133.6307   $133.63   $133.65   $133.60  
  Purchase #7 $31.70   5.349%   $33.3956   $33.40   $33.40   $33.40  
  7 purchase totals = $917.59       $1,008.8552   $1,008.86   $1,008.90   $1,008.80