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 $53.67   11.437%   $59.8082   $59.81   $59.80   $59.80  
  Purchase #2 $103.61   5.299%   $109.1003   $109.10   $109.10   $109.10  
  Purchase #3 $219.80   12.462%   $247.1915   $247.19   $247.20   $247.20  
  Purchase #4 $207.96   8.817%   $226.2958   $226.30   $226.30   $226.30  
  Purchase #5 $75.57   7.408%   $81.1682   $81.17   $81.15   $81.20  
  Purchase #6 $168.61   4.418%   $176.0592   $176.06   $176.05   $176.10  
  Purchase #7 $110.95   11.779%   $124.0188   $124.02   $124.00   $124.00  
  7 purchase totals = $940.17       $1,023.6420   $1,023.65   $1,023.60   $1,023.70