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 $140.95   7.376%   $151.3465   $151.35   $151.35   $151.30  
  Purchase #2 $245.56   13.173%   $277.9076   $277.91   $277.90   $277.90  
  Purchase #3 $110.65   13.289%   $125.3543   $125.35   $125.35   $125.40  
  Purchase #4 $156.55   5.828%   $165.6737   $165.67   $165.65   $165.70  
  Purchase #5 $52.76   3.368%   $54.537   $54.54   $54.55   $54.50  
  Purchase #6 $212.36   6.791%   $226.7814   $226.78   $226.80   $226.80  
  Purchase #7 $198.36   12.461%   $223.0776   $223.08   $223.10   $223.10  
  7 purchase totals = $1,117.19       $1,224.6781   $1,224.68   $1,224.70   $1,224.70