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 $221.83   6.173%   $235.5236   $235.52   $235.50   $235.50  
  Purchase #2 $64.53   7.582%   $69.4227   $69.42   $69.40   $69.40  
  Purchase #3 $202.44   5.553%   $213.6815   $213.68   $213.70   $213.70  
  Purchase #4 $238.29   13.312%   $270.0112   $270.01   $270.00   $270.00  
  Purchase #5 $145.70   3.518%   $150.8257   $150.83   $150.85   $150.80  
  Purchase #6 $171.88   5.837%   $181.9126   $181.91   $181.90   $181.90  
  Purchase #7 $61.52   10.513%   $67.9876   $67.99   $68.00   $68.00  
  7 purchase totals = $1,106.19       $1,189.3649   $1,189.36   $1,189.35   $1,189.30