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 $250.39   12.615%   $281.9767   $281.98   $282.00   $282.00  
  Purchase #2 $137.76   11.568%   $153.6961   $153.70   $153.70   $153.70  
  Purchase #3 $245.51   4.206%   $255.8362   $255.84   $255.85   $255.80  
  Purchase #4 $201.83   7.132%   $216.2245   $216.22   $216.20   $216.20  
  Purchase #5 $116.87   8.524%   $126.832   $126.83   $126.85   $126.80  
  Purchase #6 $120.68   4.424%   $126.0189   $126.02   $126.00   $126.00  
  Purchase #7 $101.59   9.463%   $111.2035   $111.20   $111.20   $111.20  
  7 purchase totals = $1,174.63       $1,271.7879   $1,271.79   $1,271.80   $1,271.70