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 $149.79   11.681%   $167.287   $167.29   $167.30   $167.30  
  Purchase #2 $194.92   12.631%   $219.5403   $219.54   $219.55   $219.50  
  Purchase #3 $197.30   3.263%   $203.7379   $203.74   $203.75   $203.70  
  Purchase #4 $26.88   8.197%   $29.0834   $29.08   $29.10   $29.10  
  Purchase #5 $239.46   5.376%   $252.3334   $252.33   $252.35   $252.30  
  Purchase #6 $83.28   13.218%   $94.288   $94.29   $94.30   $94.30  
  Purchase #7 $185.27   8.541%   $201.0939   $201.09   $201.10   $201.10  
  7 purchase totals = $1,076.90       $1,167.3639   $1,167.36   $1,167.45   $1,167.30