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 $229.68   13.327%   $260.2895   $260.29   $260.30   $260.30  
  Purchase #2 $245.57   9.542%   $269.0023   $269.00   $269.00   $269.00  
  Purchase #3 $84.51   4.831%   $88.5927   $88.59   $88.60   $88.60  
  Purchase #4 $183.80   10.364%   $202.849   $202.85   $202.85   $202.80  
  Purchase #5 $104.30   3.595%   $108.0496   $108.05   $108.05   $108.00  
  Purchase #6 $132.90   10.638%   $147.0379   $147.04   $147.05   $147.00  
  Purchase #7 $7.59   8.596%   $8.2424   $8.24   $8.25   $8.20  
  7 purchase totals = $988.35       $1,084.0634   $1,084.06   $1,084.10   $1,083.90