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 $77.45   5.403%   $81.6346   $81.63   $81.65   $81.60  
  Purchase #2 $240.87   5.597%   $254.3515   $254.35   $254.35   $254.40  
  Purchase #3 $61.90   6.427%   $65.8783   $65.88   $65.90   $65.90  
  Purchase #4 $190.42   12.275%   $213.7941   $213.79   $213.80   $213.80  
  Purchase #5 $192.79   7.115%   $206.507   $206.51   $206.50   $206.50  
  Purchase #6 $147.53   13.644%   $167.659   $167.66   $167.65   $167.70  
  Purchase #7 $31.35   10.336%   $34.5903   $34.59   $34.60   $34.60  
  7 purchase totals = $942.31       $1,024.4148   $1,024.41   $1,024.45   $1,024.50