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 $54.79   8.727%   $59.5715   $59.57   $59.55   $59.60  
  Purchase #2 $185.67   12.532%   $208.9382   $208.94   $208.95   $208.90  
  Purchase #3 $183.80   3.249%   $189.7717   $189.77   $189.75   $189.80  
  Purchase #4 $128.54   7.801%   $138.5674   $138.57   $138.55   $138.60  
  Purchase #5 $52.69   7.411%   $56.5949   $56.59   $56.60   $56.60  
  Purchase #6 $184.97   12.312%   $207.7435   $207.74   $207.75   $207.70  
  Purchase #7 $60.31   6.122%   $64.0022   $64.00   $64.00   $64.00  
  7 purchase totals = $850.77       $925.1894   $925.18   $925.15   $925.20