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 $100.46   10.820%   $111.3298   $111.33   $111.35   $111.30  
  Purchase #2 $126.61   4.200%   $131.9276   $131.93   $131.95   $131.90  
  Purchase #3 $172.72   4.603%   $180.6703   $180.67   $180.65   $180.70  
  Purchase #4 $146.68   7.183%   $157.216   $157.22   $157.20   $157.20  
  Purchase #5 $163.88   10.650%   $181.3332   $181.33   $181.35   $181.30  
  Purchase #6 $197.93   13.210%   $224.0766   $224.08   $224.10   $224.10  
  Purchase #7 $23.61   6.681%   $25.1874   $25.19   $25.20   $25.20  
  7 purchase totals = $931.89       $1,011.7409   $1,011.75   $1,011.80   $1,011.70