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 $47.42   10.390%   $52.3469   $52.35   $52.35   $52.30  
  Purchase #2 $163.94   4.309%   $171.0042   $171.00   $171.00   $171.00  
  Purchase #3 $228.43   11.444%   $254.5715   $254.57   $254.55   $254.60  
  Purchase #4 $37.87   8.342%   $41.0291   $41.03   $41.05   $41.00  
  Purchase #5 $86.88   11.310%   $96.7061   $96.71   $96.70   $96.70  
  Purchase #6 $243.29   4.535%   $254.3232   $254.32   $254.30   $254.30  
  Purchase #7 $130.51   10.492%   $144.2031   $144.20   $144.20   $144.20  
  7 purchase totals = $938.34       $1,014.1841   $1,014.18   $1,014.15   $1,014.10