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 $171.44   7.688%   $184.6203   $184.62   $184.60   $184.60  
  Purchase #2 $216.50   6.584%   $230.7544   $230.75   $230.75   $230.80  
  Purchase #3 $156.72   12.682%   $176.5952   $176.60   $176.60   $176.60  
  Purchase #4 $166.79   12.289%   $187.2868   $187.29   $187.30   $187.30  
  Purchase #5 $163.59   12.500%   $184.0388   $184.04   $184.05   $184.00  
  Purchase #6 $33.57   12.645%   $37.8149   $37.81   $37.80   $37.80  
  Purchase #7 $54.46   4.375%   $56.8426   $56.84   $56.85   $56.80  
  7 purchase totals = $963.07       $1,057.9530   $1,057.95   $1,057.95   $1,057.90