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 $228.84   13.626%   $260.0217   $260.02   $260.00   $260.00  
  Purchase #2 $207.69   7.835%   $223.9625   $223.96   $223.95   $224.00  
  Purchase #3 $183.52   13.670%   $208.6072   $208.61   $208.60   $208.60  
  Purchase #4 $193.47   6.829%   $206.6821   $206.68   $206.70   $206.70  
  Purchase #5 $16.30   3.613%   $16.8889   $16.89   $16.90   $16.90  
  Purchase #6 $165.29   9.687%   $181.3016   $181.30   $181.30   $181.30  
  Purchase #7 $132.84   13.167%   $150.331   $150.33   $150.35   $150.30  
  7 purchase totals = $1,127.95       $1,247.7950   $1,247.79   $1,247.80   $1,247.80