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 $64.40   6.119%   $68.3406   $68.34   $68.35   $68.30  
  Purchase #2 $245.44   9.619%   $269.0489   $269.05   $269.05   $269.00  
  Purchase #3 $197.99   11.435%   $220.6302   $220.63   $220.65   $220.60  
  Purchase #4 $185.73   9.149%   $202.7224   $202.72   $202.70   $202.70  
  Purchase #5 $57.34   12.687%   $64.6147   $64.61   $64.60   $64.60  
  Purchase #6 $135.82   5.168%   $142.8392   $142.84   $142.85   $142.80  
  Purchase #7 $135.96   7.627%   $146.3297   $146.33   $146.35   $146.30  
  7 purchase totals = $1,022.68       $1,114.5257   $1,114.52   $1,114.55   $1,114.30